U.S. patent application number 11/495821 was filed with the patent office on 2007-02-22 for collapsible force sensor coupling.
This patent application is currently assigned to Silverbrook Research Pty Ltd. Invention is credited to Attila Bertok, Tobin Allen King, Paul Lapstun, Kia Silverbrook, Matthew John Underwood.
Application Number | 20070042620 11/495821 |
Document ID | / |
Family ID | 37694461 |
Filed Date | 2007-02-22 |
United States Patent
Application |
20070042620 |
Kind Code |
A1 |
Lapstun; Paul ; et
al. |
February 22, 2007 |
Collapsible force sensor coupling
Abstract
A force sensor particularly suited for use in an electronic
stylus that senses the contact force on its nib for recording pen
strokes and handwriting recognition. The sensor has a housing for a
load bearing member for receiving an input force to be sensed and
associated circuitry for converting the input force into an output
signal indicative of the input force. A coupling transmits the
input force to the load bearing member. The coupling has an inner
section for transmitting the input force to the load bearing
member, an outer section for receiving an applied contact force and
a collapsible section for allowing the outer section to move
relative to the inner section when the contact force exceeds a
threshold. This protects the force sensor from damage by sharp
impact loads such as dropping the stylus on its nib.
Inventors: |
Lapstun; Paul; (Balmain,
AU) ; Bertok; Attila; (Balmain, AU) ; King;
Tobin Allen; (Balmain, AU) ; Underwood; Matthew
John; (Balmain, AU) ; Silverbrook; Kia;
(Balmain, AU) |
Correspondence
Address: |
SILVERBROOK RESEARCH PTY LTD
393 DARLING STREET
BALMAIN
NSW 2041
AU
|
Assignee: |
Silverbrook Research Pty
Ltd
|
Family ID: |
37694461 |
Appl. No.: |
11/495821 |
Filed: |
July 31, 2006 |
Current U.S.
Class: |
439/157 |
Current CPC
Class: |
G01L 1/26 20130101; B43K
23/126 20130101; B43K 29/10 20130101; G06F 3/03545 20130101; B43K
7/005 20130101; B43K 23/12 20130101; G06F 3/0321 20130101; B43K
7/02 20130101; B43K 29/00 20130101; B43K 29/003 20130101; B43K
29/004 20130101; G01L 5/162 20130101; B43K 29/08 20130101; B43K
29/093 20130101; B43K 25/022 20130101 |
Class at
Publication: |
439/157 |
International
Class: |
H01R 13/62 20060101
H01R013/62 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 19, 2005 |
AU |
2005904511 |
Claims
1. A force sensor assembly comprising: a load bearing member for
receiving an input force to be sensed; circuitry for converting the
input force into an output signal indicative of the input force; a
coupling having an inner section for transmitting the input force
to the load bearing member, an outer section for receiving an
applied contact force and a collapsible section for allowing the
outer section to move relative to the inner section when the
contact force exceeds a threshold.
2. A force sensor assembly according to claim 1 wherein the
collapsible section has a deformable structure.
3. A force sensor assembly according to claim 2 wherein the
deformable structure deforms plastically when the contact force
exceeds a threshold.
4. A force sensor assembly according to claim 3 wherein the
deformable structure is a series of struts extending between the
inner section and the outer section such that the struts buckle
when the contact force exceeds their combined buckling loads.
5. A force sensor assembly according to claim 4 wherein the struts
are inclined to the direction of the contact force in order to
promote buckling at a lower threshold.
6. A force sensor assembly according to claim 2 wherein the
deformable structure deforms elastically when the contact force
exceeds a threshold.
7. A force sensor assembly according to claim 6 wherein the
deformable structure has a pair of abutting slip surfaces biased
against eachother by a resilient member, such that the slip
surfaces slide relative to each other if the input force exceeds
the threshold created by friction between the slip surfaces.
8. A force sensor assembly according to claim 7 wherein the
resilient member is an elastic sleeve tightly fitted around the two
components that respectively define the slip surfaces, the slip
surfaces being inclined relative to the direction of the input
force.
9. A force sensor assembly according to claim 1 wherein the
coupling is biased against the load bearing member.
10. An electronic stylus comprising: an elongate body; a nib
extending from one end of the elongate body; and, a load bearing
member mounted to the elongate body for receiving an input force
caused by contact on the nib; circuitry for converting the input
force into an output signal indicative of the input force; a
coupling having an inner section for transmitting the input force
to the load bearing member, an outer section for receiving the
contact force on the nib and a collapsible section for allowing the
outer section to move relative to the inner section when the
contact force exceeds a threshold.
11. An electronic stylus according to claim 10 wherein the
collapsible section has a deformable structure.
12. An electronic stylus according to claim 11 wherein the
deformable structure deforms plastically when the contact force
exceeds a threshold.
13. An electronic stylus according to claim 12 wherein the
deformable structure is a series of struts extending between the
inner section and the outer section such that the struts buckle
when the contact force exceeds their combined buckling loads.
14. An electronic stylus according to claim 13 wherein the struts
are inclined to the direction of the contact force in order to
promote buckling at a lower threshold.
15. An electronic stylus according to claim 11 wherein the
deformable structure deforms elastically when the contact force
exceeds a threshold.
16. An electronic stylus according to claim 15 wherein the
deformable structure has a pair of abutting slip surfaces biased
against eachother by a resilient member, such that the slip
surfaces slide relative to each other if the input force exceeds
the threshold created by friction between the slip surfaces.
17. An electronic stylus according to claim 16 wherein the
resilient member is an elastic sleeve tightly fitted around the two
components that respectively define the slip surfaces, the slip
surfaces being inclined relative to the direction of the input
force.
18. An electronic stylus according to claim 10 wherein the coupling
is biased against the load bearing member.
19. An electronic stylus according to claim 10 wherein the nib of
the electronic stylus is a ball point writing nib with a tubular
ink cartridge extending from the nib toward the load bearing member
such that the coupling is a detachable boot that fits over the end
of the cartridge opposite the nib.
20. An electronic stylus according to claim 10 wherein the output
signal from the circuitry support a hand writing recognition
facility.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the fields of interactive
paper, printing systems, computer publishing, computer
applications, human-computer interfaces using styli with force
sensors and information appliances.
CO-PENDING APPLICATIONS
[0002] The following applications have been filed by the Applicant
simultaneously with the present application: [0003] NPS120US
NPS121US NPS122US NPS124US SBF004US SBF005US FNE027US FNE028US
FNE029US
[0004] The disclosures of these co-pending applications are
incorporated herein by reference. The above applications have been
identified by their filing docket number, which will be substituted
with the corresponding application number, once assigned.
CROSS REFERENCES
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SBF003US
[0007] The disclosures of these applications and patents are
incorporated herein by reference. Some of the above applications
have been identified by their filing docket number, which will be
substituted with the corresponding application number, once
assigned.
BACKGROUND OF THE INVENTION
[0008] The Netpage system involves the interaction between a user
and a computer network (or stand alone computer) via a pen and
paper based interface. The `pen` is an electronic stylus with a
marking or non-marking nib and an optical sensor for reading a
pattern of coded data on the paper (or other surface).
[0009] The Netpage pen is an electronic stylus with force sensing,
optical sensing and Bluetooth communication assemblies. A
significant number of electronic components need to be housed
within the pen casing together with a battery large enough to
provide a useful battery life. Despite this, the overall dimensions
of the pen need to be small enough for a user to manipulate it as
they would a normal pen.
[0010] The force sensor circuitry typically utilizes a
piezo-electric element. The sensor deflects a small amount when it
is subjected to a force. If the force applied to the sensor exceeds
the elastic limits of the sensor, and in particular the delicate
crystal element, the sensor can break. Protective stops or buffers
can be used so that a static input force can not excessively deform
the sensor. However, shock loading can still damage in the sensor,
particularly if the Netpage pen is dropped on its nib.
SUMMARY OF THE INVENTION
[0011] Accordingly, this aspect provides a pen comprising:
[0012] an elongate chassis moulding; and,
[0013] a cartridge with a nib and an elongate body; wherein,
[0014] the cartridge is configured for insertion and removal from
the elongate chassis moulding from a direction transverse to the
longitudinal axis of the chassis moulding.
[0015] According to a closely related aspect, the present invention
provides an ink cartridge for a pen, the ink cartridge
comprising:
[0016] an elongate ink reservoir; and,
[0017] a writing nib in fluid communication with the ink reservoir;
wherein,
[0018] the elongate ink reservoir has an enlarged transverse cross
section along a portion of its length intermediate its ends.
[0019] By configuring the pen chassis and cartridge so that it can
be inserted and removed from the side rather than through the ends,
the capacity of the cartridge can be significantly increased. An
enlarged section between the ends of the ink cartridge increases
the capacity while allowing the relatively thin ends to be
supported at the nib moulding and opposing end of the pen chassis.
In a Netpage pen, inserting the cartridge from the side avoids the
need to remove the force sensor when replacing the cartridge.
Again, the thinner sections at each end of the cartridge allow it
to engage a ball point nib supported in the nib moulding and
directly engage the force sensor at the other end, while the
enlarged middle portion increases the ink capacity.
[0020] Optionally, the cartridge is an ink cartridge and the
elongate body houses an ink reservoir. Preferably, the pen is an
electronic stylus with a force sensor assembly, and the cartridge
is held in the stylus such that the nib is at one end of the
elongate body and the other end of the elongate body engages the
force sensor assembly. In some embodiments, the force sensor
assembly has a load bearing member to receive an input force to be
sensed and circuitry for converting the input force into an output
signal indicative of the input force, the load bearing member
abutting the opposite end of the elongate cartridge such that the
input force comprises the axial component of the contact force on
the nib transferred by the cartridge.
[0021] Preferably the elongate cartridge is biased against the load
bearing member. In a further preferred form, the elongate cartridge
has a flange surface proximate the nib end, and a biasing element
between the flange surface and the chassis moulding biases the
elongate cartridge against the load bearing member. Typically, this
bias is between 0.1 Newtons and 0.2 Newtons (approx. 10 g-20
g).
[0022] Preferably, the circuitry is a piezoresistive bridge
circuit. However, the circuitry could also be a capacitative or
inductive force sensing circuit. In another option, the circuitry
may be an optical force sensor. In a further preferred form, the
load bearing member has a protrusion with round end for engagement
with the cartridge. In another preferred form, the cartridge has a
similar protrusion extending centrally from its end such that the
distal end of the protrusion engages the rounded end of the
protrusion from the load bearing member. In a particularly
preferred form, the housing defines a recess for the circuitry, the
rounded end of the protrusion from the load bearing member extends
proud of the recess for engaging the cartridge. Preferably, a stop
surface positioned around the opening to the recess engages the
cartridge to limit elastic deformation of the force sensor
assembly.
[0023] Typically, the force sensor assembly is configured to sense
a maximum force of 5 Newtons (approx. 500 g). Preferaby, the load
bearing member can move up to 100 microns relative to the
chassis.
[0024] In a particularly preferred embodiment, the output signal
from the circuitry support a hand writing recognition facility.
[0025] In a second aspect the present invention provides a force
sensor assembly comprising:
[0026] a load bearing member for receiving an input force;
[0027] a sensor circuit for converting the input force into a
signal indicative of the input force; and,
[0028] a force transfer coupling for receiving an applied force and
at least partially transferring it to the load bearing member as
the input force; wherein,
[0029] the applied force and the input force are not co-linear.
[0030] According to a closely related aspect, the present invention
provides an electronic stylus comprising:
[0031] an elongate body;
[0032] a nib extending from one end of the elongate body;
[0033] a load bearing member for receiving an input force;
[0034] a sensor circuit for converting the input force into a
signal indicative of the input force; and,
[0035] a force transfer coupling for receiving an applied force
caused by contact on the nib, and at least partially transferring
it to the load bearing member as the input force; wherein during
use,
[0036] the applied force and the input force are not co-linear.
[0037] With the use of a force transfer coupling, the sensor
circuitry and load bearing member can remain fixed in the pen body
while the ink cartridge is removed and replace. The force transfer
coupling may need to be removed or shifted when the ink cartridge
for the nib is being changed (assuming the stylus has a ball point
nib) but there is less potential for damage to the force sensor.
The deceleration shock from being bumped or dropped in its nib can
break the sensor circuitry, which necessitates the replacement of
the entire PCB.
[0038] Preferably, the force transfer coupling is an element
configured for elastic deformation in a direction skew to the
applied force. In a further preferred form, the element is a double
bowed section that bows outwardly when axially compressed by the
applied force. In a particularly preferred form, the load bearing
member engages one of the bowed sections at its mid point such that
the input force is perpendicular to the applied force. Preferably,
the bowed section that does not contact the load bearing member is
constrained against lateral displacement in order to stiffen the
other bowed section. In some embodiments, the bowed sections have
an arcuate lateral cross section to reduce contact friction with
the load bearing member and the lateral constraint. Optionally, the
load bearing member a rounded protrusion for contacting the bowed
section of the force transfer coupling.
[0039] In some embodiments, the force transfer coupling is a
hydraulic element that uses the applied force to create hydraulic
pressure acting on the load bearing member. In a particularly
preferred form, the hydraulic pressure acts such that the input
force is perpendicular to the applied force. Preferably, the
hydraulic fluid has low viscosity and low shear forces. In some
embodiments, the hydraulic fluid is a silicon gel. Preferably the
hydraulic fluid is contained in a reservoir at least partially
defined by a flexible membrane such that the applied force acts on
the hydraulic fluid via the flexible membrane. Optionally, the
hydraulic fluid acts directly on the load bearing member. In some
preferred embodiments, the circuitry is a piezoresistive bridge
circuit. Optionally, the nib of the electronic stylus is a ball
point writing nib with a tubular ink cartridge extending from the
nib toward the load bearing member such that the end of the
cartridge opposite the nib transmits the applied force to the
hydraulic coupling. Preferably, the output signal from the
circuitry support a hand writing recognition facility. Preferably
the circuitry is an integrated circuit (IC) mounted on a PCB
(printed circuit board), the plane of the PCB being parallel to the
longitudinal axis of the elongate body.
[0040] In some embodiments, the load bearing member can move up to
100 microns relative to the elongate body. Optionally, the input
force is limited to a maximum of 5 Newtons. In a particularly
preferred embodiment, the output signal from the circuitry support
a hand writing recognition facility.
[0041] In a third aspect the present invention provides a force
sensor assembly comprising:
[0042] a housing;
[0043] a load bearing member movably mounted in the housing for
receiving an input force to be sensed, the load bearing member
being biased against the direction of the input force;
[0044] a light source;
[0045] a photo-detector for sensing levels of illumination from the
light source; and,
[0046] circuitry for converting a range of illumination levels
sensed by the photo-detector into a range of output signals;
wherein,
[0047] the illumination level sensed by the photo-detector varies
with movement of the load bearing member within the housing such
that the output signal from the circuitry is indicative of the
input force.
[0048] According to a closely related aspect, the present invention
provides an electronic stylus comprising:
[0049] an elongate body;
[0050] a nib extending from one end of the elongate body;
[0051] a load bearing member movably mounted to the elongate body
for receiving an input force caused by contact on the nib, the load
bearing member being biased against the direction of the input
force;
[0052] a light source;
[0053] a photo-detector for sensing levels of illumination from the
light source; and,
[0054] circuitry for converting a range of illumination levels
sensed by the photo-detector into a range of output signals;
wherein,
[0055] the illumination level sensed by the photo-detector varies
with movement of the load bearing member within the elongate such
that the output signal from the circuitry is indicative of the
input force.
[0056] Using an optical force sensor is more robust than a
piezo-resistive sensor. Installing an LED and photo-detector is
less complex than the delicate requirements of a piezo-electric
crystal. The full force deflection on the nib is relatively small,
so the tolerancing in a piezo-resistive component needs to be high
enough to prevent breakage.
[0057] Preferably, the light source is fixed to the housing for
illuminating at least part of the load bearing member. Preferably,
the photo-detector is mounted to the housing such that the load
bearing member moves between the light source and the
photo-detector. In a further preferred form, the load bearing
member has an aperture through which light from the light source
can illuminate the photo-detector, the aperture being positioned
between the light source and the photo-detector at part of the load
bearing member's travel within the housing. In a particularly
preferred form, the load bearing member is biased with a spring,
the spring having a spring constant equal to the maximum force the
sensor is to sense, divided by the length in the direction of
travel within the housing of the aperture. Optionally, the aperture
is aligned with the light source and the photo-detector when the
input force is the maximum force, and the load bearing member fully
obscures the light source from the photo-detector when the input
force is zero.
[0058] Conveniently, the light source is a LED. In some
embodiments, the load bearing member has a maximum travel of 100
microns within the housing. In some embodiments, the nib of the
electronic stylus is a ball point writing nib with a tubular ink
cartridge extending from the nib toward the load bearing member
such that the coupling is a detachable boot that fits over the end
of the cartridge opposite the nib.
[0059] Typically, the force sensor is configured to sense a maximum
force of 5 Newtons (approx. 500 g). In a particularly preferred
embodiment, the output signal from the circuitry support a hand
writing recognition facility.
[0060] In a fourth aspect the present invention provides a force
sensor assembly comprising:
[0061] a load bearing member for receiving an input force to be
sensed;
[0062] circuitry for converting the input force into an output
signal indicative of the input force;
[0063] a coupling having an inner section for transmitting the
input force to the load bearing member, an outer section for
receiving an applied contact force and a collapsible section for
allowing the outer section to move relative to the inner section
when the contact force exceeds a threshold.
[0064] According to a closely related aspect, the present invention
provides an electronic stylus comprising:
[0065] an elongate body;
[0066] a nib extending from one end of the elongate body; and,
[0067] a load bearing member mounted to the elongate body for
receiving an input force caused by contact on the nib;
[0068] circuitry for converting the input force into an output
signal indicative of the input force;
[0069] a coupling having an inner section for transmitting the
input force to the load bearing member, an outer section for
receiving the contact force on the nib and a collapsible section
for allowing the outer section to move relative to the inner
section when the contact force exceeds a threshold.
[0070] Inserting a collapsible section between the nib and the
force sensor will allows static and dynamic contacts loads up to a
predetermined threshold to be transmitted to the sensor. However,
any loads that exceed the threshold, regardless of whether they are
static or shock loads, will simply force the outer section of the
coupling to collapse toward the inner section. The input force at
the sensor remains at or below the threshold.
[0071] Preferably, the collapsible section has a deformable
structure. In some embodiments, the deformable structure deforms
plastically when the contact force exceeds a threshold. In one
preferred embodiment, the deformable structure is a series of
struts extending between the inner section and the outer section
such that the struts buckle when the contact force exceeds their
combined buckling loads. Optionally, the struts are inclined to the
direction of the contact force in order to promote buckling at a
lower threshold. In other embodiments, the deformable structure
deforms elastically when the contact force exceeds a threshold.
Preferably, the deformable structure has a pair of abutting slip
surfaces biased against eachother by a resilient member, such that
the slip surfaces slide relative to each other if the input force
exceeds the threshold created by friction between the slip
surfaces. In a particularly preferred form, the resilient member is
an elastic sleeve tightly fitted around the two components that
respectively define the slip surfaces, the slip surfaces being
inclined relative to the direction of the input force.
[0072] In a particularly preferred form, the coupling is biased
against the load bearing member. Typically, this bias is between
0.1 Newtons and 0.2 Newtons (approx. 10 g-20 g). In some
embodiments, the nib of the electronic stylus is a ball point
writing nib with a tubular ink cartridge extending from the nib
toward the load bearing member such that the coupling is a
detachable boot that fits over the end of the cartridge opposite
the nib.
[0073] Typically, the force sensor is configured to sense a maximum
force of 5 Newtons (approx. 500 g). Preferaby, the load bearing
member can move up to 100 microns relative to the housing.
[0074] In a particularly preferred embodiment, the output signal
from the circuitry support a hand writing recognition facility.
[0075] In a fifth aspect the present invention provides a force
sensor assembly comprising:
[0076] a housing;
[0077] a load bearing member for receiving an input force to be
sensed;
[0078] circuitry for converting the input force into an output
signal indicative of the input force;
[0079] a coupling for transmitting the input force to the load
bearing member; and,
[0080] a compressible reservoir containing dilatant fluid mounted
between the housing and the coupling to restrict the input force to
the load bearing member caused by shock loading to the
coupling.
[0081] According to a closely related aspect, the present invention
provides an electronic stylus comprising:
[0082] an elongate body;
[0083] a nib extending from one end of the elongate body; and,
[0084] a load bearing member mounted to the elongate body for
receiving an input force caused by contact on the nib;
[0085] circuitry for converting the input force into an output
signal indicative of the input force;
[0086] a coupling for transmitting the input force to the load
bearing member; and,
[0087] a compressible reservoir containing dilatant fluid mounted
between the housing and the coupling to restrict the input force to
the load bearing member caused by shock loading to the
coupling.
[0088] A dilatant (or "shear thickening") fluid is a non-Newtonian
fluid whose viscosity increases with rate of shear. At a low shear
rate the particles are able to slide past each other and the fluid
behaves as a liquid. Above a critical shear rate friction between
the particles predominates and the fluid behaves as a solid.
[0089] To prevent force sensor damage from an impulse (shock
loading), an additional stop containing a dilatant fluid can be
inserted between the element that couples the nib to the force
sensor. The dilatant fluid can be contained in a sack formed from a
flexible membrane. During normal operation of the pen the dilatant
fluid sack acts as a liquid and deforms in response to movement of
the cartridge, allowing normal forces to be transmitted from the
cartridge to the force sensor. When a damaging impulse occurs, the
dilatant fluid effectively hardens in response to the high shear
rate, preventing movement of the cartridge and thereby protecting
the force sensor.
[0090] Preferably, the compressible reservoir of dilatant fluid
maintains a gap between the load bearing member and the coupling
when the input force is not applied, and the compressible reservoir
compresses to allow the coupling to directly engage the load
bearing member with a steady application of the input force. In a
further preferred form, the compressible reservoir is secured to
the housing and the coupling, and the coupling is biased away from
the housing to maintain the gap between the coupling and load
bearing member when the input force is not applied. Preferably, the
circuitry is a piezoresistive bridge circuit. However, the
circuitry could also be a capacitative or inductive force sensing
circuit. In another option, the circuitry may be an optical force
sensor. In a further preferred form, the load bearing member has a
protrusion with round end for engagement with the coupling. In
another preferred form, the coupling has a similar protrusion
extending centrally from a flange such that the distal end of the
protrusion engages the rounded end of the protrusion from the load
bearing member, and the compressible reservoir of dilatant fluid is
positioned between the housing and the flange. In a particularly
preferred form, the housing defines a recess for the circuitry, the
rounded end of the protrusion from the load bearing member extends
proud of the recess for engaging the coupling. Preferably, the
compressible reservoir has an annular shape and is positioned
around the opening to the recess and around the central protrusion
from the flange of the coupling.
[0091] In a particularly preferred form, the coupling is biased
against the load bearing member. Typically, this bias is between
0.1 Newtons and 0.2 Newtons (approx. 10 g-20 g). In some
embodiments, the nib of the electronic stylus is a ball point
writing nib with a tubular ink cartridge extending from the nib
toward the load bearing member such that the coupling is a
detachable boot that fits over the end of the cartridge opposite
the nib.
[0092] Typically, the force sensor is configured to sense a maximum
force of 5 Newtons (approx. 500 g). Preferaby, the load bearing
member can move up to 100 microns relative to the housing.
[0093] In a particularly preferred embodiment, the output signal
from the circuitry support a hand writing recognition facility.
BRIEF DESCRIPTION OF THE DRAWINGS
[0094] Embodiments of the invention will now be described by way of
example only with reference to the accompanying drawings in
which:
[0095] FIG. 1 shows the structure of a complete tag;
[0096] FIG. 2 shows a symbol unit cell;
[0097] FIG. 3 shows nine symbol unit cells;
[0098] FIG. 4 shows the bit ordering in a symbol;
[0099] FIG. 5 shows a tag with all bits set;
[0100] FIG. 6 shows a tag group made up of four tag types;
[0101] FIG. 7 shows the continuous tiling of tag groups;
[0102] FIG. 8 shows the interleaving of codewords A, B, C & D
within a tag;
[0103] FIG. 9 shows a codeword layout;
[0104] FIG. 10 shows a tag and its eight immediate neighbours
labelled with its corresponding bit index;
[0105] FIG. 11 shows a nib and elevation of the pen held by a
user;
[0106] FIG. 12 shows the pen held by a user at a typical incline to
a writing surface;
[0107] FIG. 13 is a lateral cross section through the pen;
[0108] FIG. 14A is a bottom and nib end partial perspective of the
pen;
[0109] FIG. 14B is a bottom and nib end partial perspective with
the fields of illumination and field of view of the sensor window
shown in dotted outline;
[0110] FIG. 15 is a partial perspective of the USB cable and USB
socket in the top end of the pen;
[0111] FIG. 16 is an exploded perspective of the pen
components;
[0112] FIG. 17 is a longitudinal cross section of the pen;
[0113] FIG. 18 is a partial longitudinal cross section of the cap
placed over the nib end of the pen;
[0114] FIG. 19 is an exploded perspective of the optics
assembly;
[0115] FIG. 20 is an exploded perspective of the force sensor
assembly;
[0116] FIG. 21 is an exploded perspective of the ink cartridge tube
and nib engaging removal tool;
[0117] FIG. 22 is a partially sectioned perspective of a new ink
cartridge engaging the nib end of the currently installed ink
cartridge;
[0118] FIG. 23 is a partial perspective of the packaged force
sensor on the main PCB;
[0119] FIG. 24 is a longitudinal cross section of the force sensor
and main PCB shown in FIG. 15;
[0120] FIG. 25 is an exploded perspective of the cap assembly;
[0121] FIG. 26 is a circuit diagram of the pen USB and power
CCT's;
[0122] FIG. 27A is a partial longitudinal cross section of the nib
and barrel molding;
[0123] FIG. 27B is a partial longitudinal cross section of the IR
LED's and the barrel molding;
[0124] FIG. 28 is a ray trace of the pen optics adjacent a sketch
of the ink cartridge;
[0125] FIG. 29 is a side elevation of the lens;
[0126] FIG. 30 is a side elevation of the nib and the field of view
of the optical sensor;
[0127] FIG. 31 is an exploded perspective of the pad;
[0128] FIG. 32 is a longitudinal cross section of the pad with the
pen inserted;
[0129] FIG. 33 is a schematic representation of the force sensor
assembly;
[0130] FIG. 34 is a schematic representation of a top-loading ink
cartridge and force sensor;
[0131] FIG. 35 is a schematic representation of a top loading ink
cartridge into a pen with a retaining cavity for the pre-load
spring;
[0132] FIG. 36 is a schematic representation of a double-bow
right-angle force sensor coupling;
[0133] FIG. 37A is a schematic representation of a hydraulic force
sensor coupling;
[0134] FIG. 37B is a longitudinal section of the hydraulic force
sensor coupling shown in FIG. 37A;
[0135] FIG. 38 is schematic representation of an alternative
configuration of the hydraulic force sensor coupling;
[0136] FIG. 39A is a more detailed sketch of the hydraulic coupling
between the cartridge and the force sensor;
[0137] FIG. 39B is a section view taken along line 39-39 of FIG.
39A;
[0138] FIG. 40 is a schematic section view of the input force
acting on the plunger and the detail of the force sensor
mounting;
[0139] FIG. 41 is a schematic section view of an alternative force
senor mounting without the input ball bearing;
[0140] FIG. 42 is a schematic section view of the force sensor chip
deflection profile;
[0141] FIG. 43 is a schematic section view of the pressure sensor
chip deflection profile;
[0142] FIG. 44 is a schematic section view of the force sensor
using pressure sensor chip and hydraulic coupling;
[0143] FIG. 45 is a plot of sensed force versus time for an input
impulse (tap) to the cartridge;
[0144] FIGS. 46A to 46C are schematic section views of input
mechanisms for the hydraulic coupling;
[0145] FIGS. 47A to 47C are schematic section views of input
mechanisms using a welded membrane;
[0146] FIG. 48 is schematic section view of the force sensor with a
stop surface directly referenced to the back surface of the sensor
chip;
[0147] FIG. 49 is a more detailed section view of the force sensor
with its stop surface directly referenced to the back surface of
the sensor chip;
[0148] FIG. 50 is schematic section view of a stop surface
arrangement for the force input mechanism of the hydraulic
coupling;
[0149] FIG. 51 is pen cartridge with collapsible element in an
un-collapsed state;
[0150] FIG. 52 is pen cartridge with collapsible element in a
collapsed state;
[0151] FIG. 53 is a stick friction collapsible element in
un-collapsed state;
[0152] FIG. 54 is a stick friction collapsible element in collapsed
state;
[0153] FIG. 55 is a sectioned perspective view of a stick friction
collapsible element in an un-collapsed state;
[0154] FIG. 56A is a plan view of an optical force sensor;
[0155] FIG. 56B is an elevation of an optical force sensor;
[0156] FIG. 57 is a high-level block diagram of the operation of
the optical force sensor;
[0157] FIG. 58 is a schematic section of a dilatant fluid o-ring to
prevent impulse damage to force sensor;
[0158] FIG. 59 is a schematic section showing boot or cartridge
with protrusion to accommodate thicker O-ring;
[0159] FIG. 60 is a block diagram of the pen electronics;
[0160] FIG. 61 show the charging and connection options for the pen
and the pod;
[0161] FIGS. 62A to 62E show the various components of the packaged
force sensor;
[0162] FIG. 63 is a bottom perspective of the main PCB with the
Bluetooth antenna shield removed;
[0163] FIG. 64 is a top perspective of the main PCB;
[0164] FIG. 65 is a bottom perspective of the chassis molding and
elastomeric and cap;
[0165] FIG. 66A is a perspective of the optics assembly lifted from
the chassis molding;
[0166] FIG. 66B is an enlarged partial perspective of the optics
assembly seated in the chassis molding;
[0167] FIG. 67A is a bottom perspective of the force sensor
assembly partially installed in the chassis molding;
[0168] FIG. 67B is a bottom perspective of the force sensing
assembly installed in the chassis molding;
[0169] FIG. 68 is a bottom perspective of the battery and main PCB
partially installed in the chassis molding;
[0170] FIG. 69 is a bottom perspective of the chassis molding with
the base molding lifted clear;
[0171] FIGS. 70A and 70B are enlarged partial perspectives showing
the cold stake on the chassis molding being swaged and sealed to
the base molding;
[0172] FIG. 71 is a bottom perspective of the product label being
fixed to the base molding;
[0173] FIG. 72 is an enlarged partial perspective of the nib
molding being inserted on the chassis molding;
[0174] FIG. 73 is a perspective of the tube molding being inserted
over the chassis molding;
[0175] FIG. 74 is a perspective of the cap assembly being placed on
the nib molding;
[0176] FIG. 75 is a diagram of the major power states of the pen;
and,
[0177] FIG. 76 is a diagram of the operational states of the
Bluetooth module.
DETAILED DESCRIPTION
[0178] As discussed above, the invention is well suited for
incorporation in the Assignee's Netpage system. In light of this,
the invention has been described as a component of a broader
Netpage architecture. However, it will be readily appreciated that
electronic styli have much broader application in many different
fields. Accordingly, the present invention is not restricted to a
Netpage context.
Netpage Surface Coding
Introduction
[0179] This section defines a surface coding used by the Netpage
system (described in co-pending application Docket No. NPS110US as
well as many of the other cross referenced documents listed above)
to imbue otherwise passive surfaces with interactivity in
conjunction with Netpage sensing devices (described below).
[0180] When interacting with a Netpage coded surface, a Netpage
sensing device generates a digital ink stream which indicates both
the identity of the surface region relative to which the sensing
device is moving, and the absolute path of the sensing device
within the region.
Surface Coding
[0181] The Netpage surface coding consists of a dense planar tiling
of tags. Each tag encodes its own location in the plane. Each tag
also encodes, in conjunction with adjacent tags, an identifier of
the region containing the tag. In the Netpage system, the region
typically corresponds to the entire extent of the tagged surface,
such as one side of a sheet of paper.
[0182] Each tag is represented by a pattern which contains two
kinds of elements. The first kind of element is a target. Targets
allow a tag to be located in an image of a coded surface, and allow
the perspective distortion of the tag to be inferred. The second
kind of element is a macrodot. Each macrodot encodes the value of a
bit by its presence or absence.
[0183] The pattern is represented on the coded surface in such a
way as to allow it to be acquired by an optical imaging system, and
in particular by an optical system with a narrowband response in
the near-infrared. The pattern is typically printed onto the
surface using a narrowband near-infrared ink.
Tag Structure
[0184] FIG. 1 shows the structure of a complete tag 200. Each of
the four black circles 202 is a target. The tag 200, and the
overall pattern, has four-fold rotational symmetry at the physical
level.
[0185] Each square region represents a symbol 204, and each symbol
represents four bits of information. Each symbol 204 shown in the
tag structure has a unique label 216. Each label 216 has an
alphabetic prefix and a numeric suffix. FIG. 2 shows the structure
of a symbol 204. It contains four macrodots 206, each of which
represents the value of one bit by its presence (one) or absence
(zero).
[0186] The macrodot 206 spacing is specified by the parameter s
throughout this specification. It has a nominal value of 143 .mu.m,
based on 9 dots printed at a pitch of 1600 dots per inch. However,
it is allowed to vary within defined bounds according to the
capabilities of the device used to produce the pattern.
[0187] FIG. 3 shows an array 208 of nine adjacent symbols 204. The
macrodot 206 spacing is uniform both within and between symbols
208.
[0188] FIG. 4 shows the ordering of the bits within a symbol
204.
[0189] Bit zero 210 is the least significant within a symbol 204;
bit three 212 is the most significant. Note that this ordering is
relative to the orientation of the symbol 204. The orientation of a
particular symbol 204 within the tag 200 is indicated by the
orientation of the label 216 of the symbol in the tag diagrams (see
for example FIG. 1). In general, the orientation of all symbols 204
within a particular segment of the tag 200 is the same, consistent
with the bottom of the symbol being closest to the centre of the
tag.
[0190] Only the macrodots 206 are part of the representation of a
symbol 204 in the pattern. The square outline 214 of a symbol 204
is used in this specification to more clearly elucidate the
structure of a tag 204. FIG. 5, by way of illustration, shows the
actual pattern of a tag 200 with every bit 206 set. Note that, in
practice, every bit 206 of a tag 200 can never be set.
[0191] A macrodot 206 is nominally circular with a nominal diameter
of ( 5/9)s. However, it is allowed to vary in size by .+-.10%
according to the capabilities of the device used to produce the
pattern.
[0192] A target 202 is nominally circular with a nominal diameter
of ( 17/9)s. However, it is allowed to vary in size by .+-.10%
according to the capabilities of the device used to produce the
pattern.
[0193] The tag pattern is allowed to vary in scale by up to .+-.10%
according to the capabilities of the device used to produce the
pattern. Any deviation from the nominal scale is recorded in the
tag data to allow accurate generation of position samples.
Tag Groups
[0194] Tags 200 are arranged into tag groups 218. Each tag group
contains four tags arranged in a square. Each tag 200 has one of
four possible tag types, each of which is labelled according to its
location within the tag group 218. The tag type labels 220 are 00,
10, 01 and 11, as shown in FIG. 6.
[0195] FIG. 7 shows how tag groups are repeated in a continuous
tiling of tags, or tag pattern 222. The tiling guarantees the any
set of four adjacent tags 200 contains one tag of each type
220.
Codewords
[0196] The tag contains four complete codewords. The layout of the
four codewords is shown in FIG. 8. Each codeword is of a punctured
2.sup.4-ary (8, 5) Reed-Solomon code. The codewords are labelled A,
B, C and D. Fragments of each codeword are distributed throughout
the tag 200.
[0197] Two of the codewords are unique to the tag 200. These are
referred to as local codewords 224 and are labelled A and B. The
tag 200 therefore encodes up to 40 bits of information unique to
the tag.
[0198] The remaining two codewords are unique to a tag type, but
common to all tags of the same type within a contiguous tiling of
tags 222. These are referred to as global codewords 226 and are
labelled C and D, subscripted by tag type. A tag group 218
therefore encodes up to 160 bits of information common to all tag
groups within a contiguous tiling of tags.
Reed-Solomon Encoding
[0199] Codewords are encoded using a punctured 2.sup.4-ary (8, 5)
Reed-Solomon code. A 2.sup.4-ary (8, 5) Reed-Solomon code encodes
20 data bits (i.e. five 4-bit symbols) and 12 redundancy bits (i.e.
three 4-bit symbols) in each codeword. Its error-detecting capacity
is three symbols. Its error-correcting capacity is one symbol.
[0200] FIG. 9 shows a codeword 228 of eight symbols 204, with five
symbols encoding data coordinates 230 and three symbols encoding
redundancy coordinates 232. The codeword coordinates are indexed in
coefficient order, and the data bit ordering follows the codeword
bit ordering.
[0201] A punctured 2.sup.4-ary (8, 5) Reed-Solomon code is a
2.sup.4-ary (15, 5) Reed-Solomon code with seven redundancy
coordinates removed. The removed coordinates are the most
significant redundancy coordinates.
[0202] The code has the following primitive polynominal:
p(x)=x.sup.4+x+1 (EQ 1)
[0203] The code has the following generator polynominal:
g(x)=(x+.alpha.)(x+.alpha..sup.2) . . . (x+.alpha..sup.10) (EQ
2)
[0204] For a detailed description of Reed-Solomon codes, refer to
Wicker, S. B. and V. K. Bhargava, eds., Reed-Solomon Codes and
Their Applications, IEEE Press, 1994, the contents of which are
incorporated herein by reference.
The Tag Coordinate Space
[0205] The tag coordinate space has two orthogonal axes labelled x
and y respectively. When the positive x axis points to the right,
then the positive y axis points down.
[0206] The surface coding does not specify the location of the tag
coordinate space origin on a particular tagged surface, nor the
orientation of the tag coordinate space with respect to the
surface. This information is application-specific. For example, if
the tagged surface is a sheet of paper, then the application which
prints the tags onto the paper may record the actual offset and
orientation, and these can be used to normalise any digital ink
subsequently captured in conjunction with the surface.
[0207] The position encoded in a tag is defined in units of tags.
By convention, the position is taken to be the position of the
centre of the target closest to the origin.
Tag Information Content
[0208] Table I defines the information fields embedded in the
surface coding. Table 2 defines how these fields map to codewords.
TABLE-US-00001 TABLE 1 field width description per codeword
codeword type 2 The type of the codeword, i.e. one of A(b'00'), B
(b'01'), C (b'10') and D (b'11'). per tag tag type 2 The type.sup.1
of the tag, i.e. one of 00 (b'00'), 01 (b'01'), 10 (b'10') and 11
(b'11'). x coordinate 13 The unsigned x coordinate of the
tag.sup.2. y coordinate 13 The unsigned y coordinate of the
tag.sup.b. active area flag 1 A flag indicating whether the tag is
a member of an active area. b'1' indicates membership. active area
map 1 A flag indicating whether an active area map flag is present.
b'1' indicates the presence of a map (see next field). If the map
is absent then the value of each map entry is derived from the
active area flag (see previous field). active area map 8 A
map.sup.3 of which of the tag's immediate eight neighbours are
members of an active area. b'1' indicates membership. data fragment
8 A fragment of an embedded data stream. Only present if the active
area map is absent. per tag group encoding format 8 The format of
the encoding. 0: the present encoding Other values are TBA. region
flags 8 Flags controlling the interpretation and routing of
region-related information. 0: region ID is an EPC 1: region is
linked 2: region is interactive 3: region is signed 4: region
includes data 5: region relates to mobile application Other bits
are reserved and must be zero. tag size 16 The difference between
the actual tag size adjustment and the nominal tag size.sup.4, in
10 nm units, in sign-magnitude format. region ID 96 The ID of the
region containing the tags. CRC 16 A CRC.sup.5 of tag group data.
total 320 .sup.1corresponds to the bottom two bits of the x and y
coordinates of the tag .sup.2allows a maximum coordinate value of
approximately 14 m .sup.3FIG. 29 indicates the bit ordering of the
map .sup.4the nominal tag size is 1.7145 mm (based on 1600 dpi, 9
dots per macrodot, and 12 macrodots per tag) .sup.5CCITT CRC-16
[7]
[0209] FIG. 10 shows a tag 200 and its eight immediate neighbours,
each labelled with its corresponding bit index in the active area
map. An active area map indicates whether the corresponding tags
are members of an active area. An active area is an area within
which any captured input should be immediately forwarded to the
corresponding Netpage server for interpretation. It also allows the
Netpage sensing device to signal to the user that the input will
have an immediate effect. TABLE-US-00002 TABLE 2 Mapping of fields
to codewords codeword field codeword bits field width bits A 1:0
codeword type 2 all (b'00') 10:2 x coordinate 9 12:4 19:11 y
coordinate 9 12:4 B 1:0 codeword type 2 all (b'01') 2 tag type 1 0
5:2 x coordinate 4 3:0 6 tag type 1 1 9:6 y coordinate 4 3:0 10
active area flag 1 all 11 active area map flag 1 all 19:12 active
area map 8 all 19:12 data fragment 8 all C.sub.00 1:0 codeword type
2 all (b'10') 9:2 encoding format 8 all 17:10 region flags 8 all
19:18 tag size adjustment 2 1:0 C.sub.01 1:0 codeword type 2 all
(b'10') 15:2 tag size adjustment 14 15:2 19:16 region ID 4 3:0
C.sub.10 1:0 codeword type 2 all (b'10') 19:2 region ID 18 21:4
C.sub.11 1:0 codeword type 2 all (b'10') 19:2 region ID 18 39:22
D.sub.00 1:0 codeword type 2 all (b'1') 19:2 region ID 18 57:40
D.sub.01 0:1 codeword type 2 all (b'11') 19:2 region ID 18 75:58
D.sub.10 1:0 codeword type 2 all (b'11') 19:2 region ID 18 93:76
D.sub.11 1:0 codeword type 2 all (b'11') 3:2 region ID 2 95:94 19:4
CRC 16 all
[0210] Note that the tag type can be moved into a global codeword
to maximise local codeword utilization. This in turn can allow
larger coordinates and/or 16-bit data fragments (potentially
configurably in conjunction with coordinate precision). However,
this reduces the independence of position decoding from region ID
decoding and has not been included in the specification at this
time.
Embedded Data
[0211] If the "region includes data" flag in the region flags is
set then the surface coding contains embedded data. The data is
encoded in multiple contiguous tags' data fragments, and is
replicated in the surface coding as many times as it will fit.
[0212] The embedded data is encoded in such a way that a random and
partial scan of the surface coding containing the embedded data can
be sufficient to retrieve the entire data. The scanning system
reassembles the data from retrieved fragments, and reports to the
user when sufficient fragments have been retrieved without
error.
[0213] As shown in Table 3, a 200-bit data block encodes 160 bits
of data. The block data is encoded in the data fragments of A
contiguous group of 25 tags arranged in a 5.times.5 square. A tag
belongs to a block whose integer coordinate is the tag's coordinate
divided by 5. Within each block the data is arranged into tags with
increasing x coordinate within increasing y coordinate.
[0214] A data fragment may be missing from a block where an active
area map is present. However, the missing data fragment is likely
to be recoverable from another copy of the block.
[0215] Data of arbitrary size is encoded into a superblock
consisting of a contiguous set of blocks arranged in a rectangle.
The size of the superblock is encoded in each block. A block
belongs to a superblock whose integer coordinate is the block's
coordinate divided by the superblock size. Within each superblock
the data is arranged into blocks with increasing x coordinate
within increasing y coordinate.
[0216] The superblock is replicated in the surface coding as many
times as it will fit, including partially along the edges of the
surface coding.
[0217] The data encoded in the superblock may include more precise
type information, more precise size information, and more extensive
error detection and/or correction data. TABLE-US-00003 TABLE 3
Embedded data block field width description data type 8 The type of
the data in the superblock. Values include: 0: type is controlled
by region flags 1: MIME Other values are TBA. superblock width 8
The width of the superblock, in blocks. superblock height 8 The
height of the superblock, in blocks. data 160 The block data. CRC
16 A CRC.sup.6 of the block data. total 200 .sup.6CCITT CRC-16
[7]
Cryptographic Signature of Region ID
[0218] If the "region is signed" flag in the region flags is set
then the surface coding contains a 160-bit cryptographic signature
of the region ID. The signature is encoded in a one-block
superblock.
[0219] In an online environment any signature fragment can be used,
in conjunction with the region ID, to validate the signature. In an
offline environment the entire signature can be recovered by
reading multiple tags, and can then be validated using the
corresponding public signature key. This is discussed in more
detail in Netpage Surface Coding Security section of the cross
reference co-pending application Docket No. NPS100US, which is
entirely incorporated into the application with docket no.
NPS101US.
Mime Data
[0220] If the embedded data type is "MIME" then the superblock
contains Multipurpose Internet Mail Extensions (MIME) data
according to RFC 2045 (see Freed, N., and N. Borenstein,
"Multipurpose Internet Mail Extensions (MIME)--Part One: Format of
Internet Message Bodies", RFC 2045, November 1996), RFC 2046 (see
Freed, N., and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME)--Part Two: Media Types", RFC 2046, November 1996)
and related RFCs. The MIME data consists of a header followed by a
body. The header is encoded as a variable-length text string
preceded by an 8-bit string length. The body is encoded as a
variable-length type-specific octet stream preceded by a 16-bit
size in big-endian format.
[0221] The basic top-level media types described in RFC 2046
include text, image, audio, video and application. RFC 2425 (see
Howes, T., M. Smith and F. Dawson, "A MIME Content-Type for
Directory Information", RFC 2045, September 1998) and RFC 2426 (see
Dawson, F., and T. Howes, "vCard MIME Directory Profile", RFC 2046,
September 1998) describe a text subtype for directory information
suitable, for example, for encoding contact information which might
appear on a business card.
Encoding and Printing Consideration
[0222] The Print Engine Controller (PEC) supports the encoding of
two fixed (per-page) 2.sup.4-ary (15, 5) Reed-Solomon codewords and
six variable (per-tag) 2.sup.4-ary (15, 5) Reed-Solomon codewords.
Furthermore, PEC supports the rendering of tags via a rectangular
unit cell whose layout is constant (per page) but whose variable
codeword data may vary from one unit cell to the next. PEC does not
allow unit cells to overlap in the direction of page movement. A
unit cell compatible with PEC contains a single tag group
consisting of four tags. The tag group contains a single A codeword
unique to the tag group but replicated four times within the tag
group, and four unique B codewords. These can be encoded using five
of PEC's six supported variable codewords. The tag group also
contains eight fixed C and D codewords. One of these can be encoded
using the remaining one of PEC's variable codewords, two more can
be encoded using PEC's two fixed codewords, and the remaining five
can be encoded and pre-rendered into the Tag Format Structure (TFS)
supplied to PEC.
[0223] PEC imposes a limit of 32 unique bit addresses per TFS row.
The contents of the unit cell respect this limit. PEC also imposes
a limit of 384 on the width of the TFS. The contents of the unit
cell respect this limit.
[0224] Note that for a reasonable page size, the number of variable
coordinate bits in the A codeword is modest, making encoding via a
lookup table tractable. Encoding of the B codeword via a lookup
table may also be possible. Note that since a Reed-Solomon code is
systematic, only the redundancy data needs to appear in the lookup
table.
Imaging and Decoding Considerations
[0225] The minimum imaging field of view required to guarantee
acquisition of an entire tag has a diameter of 39.6s (i.e.
(2.times.(12+2)) {square root over (2)}s), allowing for arbitrary
alignment between the surface coding and the field of view. Given a
macrodot spacing of 143 .mu.m, this gives a required field of view
of 5.7 mm.
[0226] Table 4 gives pitch ranges achievable for the present
surface coding for different sampling rates, assuming an image
sensor size of 128 pixels. TABLE-US-00004 TABLE 4 Pitch ranges
achievable for present surface coding for different sampling rates;
dot pitch = 1600 dpi, macrodot pitch = 9 dots, viewing distance =
30 mm, nib-to-FOV separation = 1 mm, image sensor size = 128 pixels
sampling rate pitch range 2 -40 to +49 2.5 -27 to +36 3 -10 to
+18
[0227] Given the present surface coding, the corresponding decoding
sequence is as follows: [0228] locate targets of complete tag
[0229] infer perspective transform from targets [0230] sample and
decode any one of tag's four codewords [0231] determine codeword
type and hence tag orientation [0232] sample and decode required
local (A and B) codewords [0233] codeword redundancy is only 12
bits, so only detect errors [0234] on decode error flag bad
position sample [0235] determine tag x-y location, with reference
to tag orientation [0236] infer 3D tag transform from oriented
targets [0237] determine nib x-y location from tag x-y location and
3D transform [0238] determine active area status of nib location
with reference to active area map [0239] generate local feedback
based on nib active area status [0240] determine tag type from A
codeword [0241] sample and decode required global (C and D)
codewords (modulo window alignment, with reference to tag type)
[0242] although codeword redundancy is only 12 bits, correct
errors; subsequent CRC verification will detect erroneous error
correction [0243] verify tag group data CRC [0244] on decode error
flag bad region ID sample [0245] determine encoding type, and
reject unknown encoding [0246] determine region flags [0247]
determine region ID [0248] encode region ID, nib x-y location, nib
active area status in digital ink [0249] route digital ink based on
region flags
[0250] Note that region ID decoding need not occur at the same rate
as position decoding.
[0251] Note that decoding of a codeword can be avoided if the
codeword is found to be identical to an already-known good
codeword.
Netpage Pen
Functional Overview
[0252] The Netpage pen is a motion-sensing writing instrument which
works in conjunction with a tagged Netpage surface (see Netpage
Surface Coding and Netpage Surface Coding Security sections above).
The pen incorporates a conventional ballpoint pen cartridge for
marking the surface, a motion sensor for simultaneously capturing
the absolute path of the pen on the surface, an identity sensor for
simultaneously identifying the surface, a force sensor for
simultaneously measuring the force exerted on the nib, and a
real-time clock for simultaneously measuring the passage of
time.
[0253] While in contact with a tagged surface, as indicated by the
force sensor, the pen continuously images the surface region
adjacent to the nib, and decodes the nearest tag in its field of
view to determine both the identity of the surface, its own
instantaneous position on the surface and the pose of the pen. The
pen thus generates a stream of timestamped position samples
relative to a particular surface, and transmits this stream to a
Netpage server (see Netpage Architecture section in co-pending
application Docket No. NPS110US). The sample stream describes a
series of strokes, and is conventionally referred to as digital ink
(DInk). Each stroke is delimited by a pen down and a pen up event,
as detected by the force sensor.
[0254] The pen samples its position at a sufficiently high rate
(nominally 100 Hz) to allow a Netpage server to accurately
reproduce hand-drawn strokes, recognise handwritten text, and
verify hand-written signatures.
[0255] The Netpage pen also supports hover mode in interactive
applications. In hover mode the pen is not in contact with the
paper and may be some small distance above the surface of the paper
(or tablet etc.). This allows the position of the pen, including
its height and pose to be reported. In the case of an interactive
application the hover mode behaviour can be used to move the cursor
without marking the paper, or the distance of the nib from the
coded surface could be used for tool behaviour control, for example
an air brush function.
[0256] The pen includes a Bluetooth radio transceiver for
transmitting digital ink via a relay device to a Netpage server.
When operating offline from a Netpage server the pen buffers
captured digital ink in non-volatile memory. When operating online
to a Netpage server the pen transmits digital ink in real time.
[0257] The pen is supplied with a docking cradle or "pod". The pod
contains a Bluetooth to USB relay. The pod is connected via a USB
cable to a computer which provides communications support for local
applications and access to Netpage services.
[0258] The pen is powered by a rechargeable battery. The battery is
not accessible to or replaceable by the user. Power to charge the
pen can be taken from the USB connection or from an external power
adapter through the pod. The pen also has a power and
USB-compatible data socket to allow it to be externally connected
and powered while in use.
[0259] The pen cap serves the dual purpose of protecting the nib
and the imaging optics when the cap is fitted and signalling the
pen to leave a power-preserving state when uncapped.
Pen Form Factor
[0260] The overall weight (45 g), size and shape (159 mm.times.17
mm) of the Netpage pen fall within the conventional bounds of
hand-held writing instruments.
Ergonomics and Layout
[0261] FIG. 11 shows a rounded triangular profile gives the pen 400
an ergonomically comfortable shape to grip and use the pen in the
correct functional orientation. It is also a practical shape for
accommodating the internal components. A normal pen-like grip
naturally conforms to a triangular shape between thumb 402, index
finger 404 and middle finger 406.
[0262] As shown in FIG. 12, a typical user writes with the pen 400
at a nominal pitch of about 30 degrees from the normal toward the
hand 408 when held (positive angle) but seldom operates a pen at
more than about 10 degrees of negative pitch (away from the hand).
The range of pitch angles over which the pen 400 is able to image
the pattern on the paper has been optimised for this asymmetric
usage. The shape of the pen 400 helps to orient the pen correctly
in the user's hand 408 and to discourage the user from using the
pen "upside-down". The pen functions "upside-down" but the
allowable tilt angle range is reduced.
[0263] The cap 410 is designed to fit over the top end of the pen
400, allowing it to be securely stowed while the pen is in use.
Multi colour LEDs illuminate a status window 412 in the top edge
(as in the apex of the rounded triangular cross section) of the pen
400 near its top end. The status window 412 remains un-obscured
when the cap is stowed. A vibration motor is also included in the
pen as a haptic feedback system (described in detail below).
[0264] As shown in FIG. 13, the grip portion of the pen has a
hollow chassis molding 416 enclosed by a base molding 528 to house
the other components. The ink cartridge 414 for the ball point nib
(not shown) fits naturally into the apex 420 of the triangular
cross section, placing it consistently with the user's grip. This
in turn provides space for the main PCB 422 in the centre of the
pen and for the battery 424 in the base of the pen. By referring to
FIG. 14a, it can be seen that this also naturally places the
tag-sensing optics 426 unobtrusively below the nib 418 (with
respect to nominal pitch). The nib molding 428 of the pen 400 is
swept back below the ink cartridge 414 to prevent contact between
the nib molding 428 and the paper surface when the pen is operated
at maximum pitch.
[0265] As best shown in FIG. 14b, the imaging field of view 430
emerges through a centrally positioned IR filter/window 432 below
the nib 418, and two near-infrared illumination LEDs 434, 436
emerge from the two bottom corners of the nib molding 428. The use
of two illumination LEDs 434, 436 ensures a more uniform
illumination field 438, 440.
[0266] As the pen is hand-held, it may be held at an angle that
causes reflections from one of the LED's that are detrimental to
the image sensor. By providing more than one LED, the LED causing
the offending reflections can be extinguished.
Pen Feedback Indications
[0267] FIG. 17 is a longitudinal cross section through the
centre-line if the pen 400 (with the cap 410 stowed on the end of
the pen). The pen incorporates red and green LEDs 444 to indicate
several states, using colours and intensity modulation. A light
pipe 448 on the LEDs 444 transmit the signal to the status
indicator window 412 in the tube molding 416. These signal status
information to the user including power-on, battery level,
untransmitted digital ink, network connection on-line, fault or
error with an action.
[0268] A vibration motor 446 is used to haptically convey
information to the user for important verification functions during
transactions. This system is used for important interactive
indications that might be missed due to inattention to the LED
indicators 444 or high levels of ambient light. The haptic system
indicates to the user when: [0269] The pen wakes from standby mode
[0270] There is an error with an action [0271] To acknowledge a
transaction Pod Feedback Indications
[0272] Turning briefly to the recharging pod 450 shown in FIGS. 31
and 32, red and green LEDs 452 to indicate various states using
colours and intensity modulation. The light from the LEDs is
transmitted to the exterior of the pod via the polymer light pipe
molding 454. These signal status information to the user including
charging state, and untransmitted digital ink by
illuminating/pulsating one LEDs 452 at a time.
Features and Accessories
[0273] As shown in FIG. 15, the pen has a power and data socket 458
is located in the top end 456 of the pen, hidden and
moisture-sealed behind an elastomeric end-cap 460. The end-cap can
be prised open to give access to the socket 458 and reset switch
(at the bottom of recess 464) and remains open while the cable 462
is in use. The USB power and data cable 462 allows the pen to be
used for periods that exceed the battery life.
[0274] The usual method of charging the pen 400 is via the charging
pod 450 shown in FIGS. 31 and 32. As will be described in greater
detail below, the pod 450 includes a Bluetooth transceiver
connected by USB to a computer and several LEDs to indicate for
charging status. The pod is compact to minimise its desktop
footprint, and has a weighted base for stability. Data transfer
occurs between the pen and the pod via a Bluetooth radio link.
Market Differentiation
[0275] Digital mobile products and quality pens are usually
considered as personal items. This pen product is used by both
genders from 5 years upwards for personal, educational and business
use, so many markets have to be catered for. The pen design allows
for substantial user customisation of the external appearance of
the pen 400 and the pod 450 by having user changeable parts, namely
the cap 410, an outer tube molding 466 (best shown in FIG. 16 and
49) and the pod jacket 468 (best shown in FIG. 31 and 32). These
parts are aquagraphic printed (a water based transfer system) to
produce a variety of high quality graphic images and textures over
all surfaces of these parts. These parts are accessories to the
pen, allowing the user to change the appearance whenever they wish.
A number of licensed images provide enhancers for the sale of
accessories as an additional business model, similar to the
practice with mobile phone covers.
Pen Mechanical Design
Parts and Assemblies
[0276] Referring to FIG. 16, the pen 400 has been designed as a
high volume product and has four major sub-assemblies: [0277] an
optical assembly 470; [0278] a force sensing assembly 474; [0279] a
cap assembly 472; and, [0280] the main assembly 476, which holds
the main PCB 422 and battery 424.
[0281] Wherever possible, moldings have been designed as
line-of-draw to reduce cost and promote longevity in the
tooling.
[0282] These assemblies and the other major parts can be identified
in FIG. 17. As the form factor of the pen is to be as small as
possible these parts are packed as closely as practical. The
electrical components in the upper part of the pen, namely the
force sensor assembly 474 and the vibration motor 446 all have
sprung contacts (512 of FIG. 24 and 480 of FIG. 62A respectively)
directly mating with contact pads 482 and 484 respectively (see
FIG. 64) on the PCB 422. This eliminates the need for connectors
and also decouples these parts from putting any stress onto the
main PCB.
[0283] Although certain individual molded parts are thin walled
(0.8 to 1.2 mm) the combination of these moldings creates a strong
structure. The pen is designed not to be user serviceable and
therefore has a cold stake under the exterior label to prevent user
entry. Non-conducting plastics moldings are used wherever possible
to allow an omnidirectional beam pattern to be formed by the
Bluetooth radio antenna 486 (see FIG. 64).
Optics Assembly
[0284] The major components of the optical assembly are as shown in
FIGS. 18 and 19. The axial alignment of the lens 488 to the image
sensor 490 is toleranced to be better than 50 .mu.m to minimise
blur at the image. The barrel molding 492 is therefore has high
precision with tight tolerancing. It has a molded-in aperture 494
near the image sensor 490, which provides the location for the lens
488. As the effect of thermal expansion is very small on a molding
this size, it is not necessary to use a more expensive
material.
[0285] The flex PCB 496 mounts two infrared LEDs 434 and 436, a
wire bonded Chip-on-Flex image sensor 490 and some chip capacitors
502. The flex PCB 496 is 75 micron thick polyimide, which allows
the two infrared LEDs 434 and 436 to be manipulated. Stiffeners are
required in certain areas on the flex as backing for the attached
components.
[0286] The flex PCB 496 is laser cut to provide accuracy for
mounting onto the barrel molding 492 and fine pitch connector
alignment.
Force Sensing Assembly and Ink Cartridge
[0287] FIGS. 20, 23, 24 and 64 show the components and installation
of the force sensing assembly. The force sensing assembly 474 is
designed to accurately measure force put on the ink cartridge 414
during use. It is specified to sense between 0 and 500 grams force
with enough fidelity to support handwriting recognition in the
Netpage services. This captive assembly has two coaxial conductive
metal tubes 498, a retainer spring 504 and a packaged force sensor
500.
Conductive Metal Tube
[0288] The conductive metal tubes 498 has an insert molded
insulation layer 506 between two metal tubes (inner tube 508 and
outer tube 510), which each have a sprung gold plated contact
finger (512 and 514 respectively). Power for charging the battery
is provided by two contacts 516 (see FIG. 31) in the charging pod
450 and is conducted by these two tubes directly to recharging
contacts 518 and 520 (see FIG. 64) on the main PCB 422, via a
spring contact (512 and 514 respectively) on each tube.
[0289] When the pen cap assembly 472 is placed on the front of the
pen 400, a conductive elastomeric molding in the pen cap mates with
the ends of both concentric tubes in the conductive metal tube
part, completing the circuit and signalling the cap presence to the
pen electronics (see FIG. 18).
Force Sensor Operating Principles
[0290] FIG. 33 schematically illustrates the operation of the force
sensing assembly 474. The spring 700 applies a pre-load to the
force sensor IC 526 (via a ball bearing 524) before the cartridge
414 is subject to any force at the nib 418.
[0291] The cartridge 414 itself is not pushed against the force
sensor as it passes through the spring. Instead, the spring pushes
a boot 702 against the force sensor, and the boot is coupled to the
end of the cartridge. The boot 702 is a compromise between allowing
easy manual insertion and removal of cartridge 414, and ensuring
the cartridge is held securely without travel. The use of a boot
702 also allows the inclusion of a stop surface 698. The stop
limits the travel of the boot 702 thereby protecting the spring 700
from overload.
Packaged Force Sensor
[0292] FIGS. 62A to 62E are perspectives of the various components
of the packaged force sensor 500. FIG. 62A shows a steel ball 524
protruding from the front of a sensor IC (chip) 526. The ball 524
is the point contact used to transmit force directly to the chip.
Wire bonds 604 connect the chip 526 to the spring contacts 478. The
chip sits in the recess 564 formed in the rear molding 566 shown in
FIG. 62B. A pressure relief vent 584 in the base of the recess 564
allows air trapped by the chip 526 to escape. The front molding 606
shown in FIG. 62C, has slots 608 in its underside for the sprung
contacts 478 and a central aperture 610 to hold the ball 524.
Location details 612 mate with corresponding details in the coaxial
conductive tubes 498 as shown in FIG. 24.
[0293] As there is only 10 microns full span movement in this
system, the mounting of this assembly in the pen and use of axial
preload is tightly toleranced. The force sensing assembly is
mounted in the top of the pen so that it can only stress the pen
chassis molding 416 (see FIG. 16), and force will not be
transmitted to the main PCB 422. The force sensor is a push fit
onto the end of the inner conductive metal tube 508 also trapping
the retainer spring 504, which makes a simple dedicated assembly
500.
Retainer Spring
[0294] Turning to FIGS. 20 and 24, the retainer spring 504 is the
equivalent to the boot 702 described in FIG. 33. It is a high
precision stamping out of thin sheet metal with an insulating layer
708 at the point where it contacts the ball 524. This inhibits
electrical interference with the force sensor IC 526 caused by
external electrostatic discharge via the ink cartridge 414. The
metal retainer spring 504 is formed into four gripping arms 530 and
two spring arms 532. A spent cartridge removal tool 534 is secured
to the open end of the cartridge 414 with an interference fit. The
gripping arms 530 grip a complementary external grip profile 704 on
the removal tool 534. The spring arms 532 extend beyond the end of
gripping arms 530 to press against the stepped section 706 in the
coaxial tube assembly 498. This in turn pushes insulated base 708
against the ball 524 to put an accurate axial preload force of
between 10 and 20 grams onto the force sensor.
Ink Cartridge
[0295] The pen ink cartridge 414 is best shown in FIGS. 21A and
21B. Research shows that industry practice is for the ballpoint nib
418 to be made by one source and the metal tube 536 to be made by
another, along with assembly and filling. There are no front
loading standard ink cartridges that meet the design capacity and
form factor requirements so a custom cartridge has been developed.
This ink cartridge 414 has a 3 mm diameter tube 536 with a standard
ballpoint nib inserted. The spent cartridge removal tool 534 is a
custom end molding that caps the open end of the metal tube
536.
[0296] The removal tool 536 contains an air vent 538 for ink flow,
a location detail 540 and a co-molded elastomeric ring 542 around a
recess 544 detail used for extracting the spent ink cartridge. The
tool is levered down to engage the nib of the old cartridge and
then drawn out through the nib end of the pen as shown in FIG. 21B.
The elastomer ring 542 reduces the possibility that a hard shock
could damage the force sensor if the pen is dropped onto a hard
surface.
[0297] The location detail 540 allows the ink cartridge 414 to
accurately seat into the retainer spring 504 in the force sensing
assembly 474 and to be preloaded against the force sensor 500. The
removal tool (apart from the co-molded elastomeric ring) is made
out of a hard plastic such as acetal and can be molded in color to
match the ink contents. The ink capacity is 5 ml giving an expected
write-out length comparable with standard ballpoint ink cartridges.
This capacity means that refill cycles will be relatively
infrequent during the lifetime of the pen.
Force Sensing Method
[0298] Pressing the nib 418 against a surface will transfer the
force to the ball 524 via the gripping arms 530. The force from the
nib adds to the preload force from the spring arms 532. The force
sensor is a push fit into the end of the coaxial tube assembly 498
and both directly connect to the PCB with spring contacts (478 and
512 respecively). FIG. 24 shows the limited space available for an
axial force sensor, hence a packaged design is required as
off-the-shelf items have no chance of fitting in this space
envelope in the required configuration.
[0299] This force sensing arrangement detects the axial force
applied to the cartridge 414, which is the simplest and most
accurate solution. There is negligible friction in the system as
the cartridge contacts only on two points, one at either end of the
conductive metal barrel 498. The metal retainer spring 504 will
produce an accurate preload force up to 20 grams onto the force
sensor 500. This is seen to be a reliable system over time, as the
main parts are metal and therefore will not suffer from creep, wear
or stiction during the lifetime of the pen.
[0300] This design also isolates the applied force by directing it
onto the packaged force sensor, which pushes against the solid seat
in the chassis molding 416 of the pen. This allows the force
sensing assembly 474 to float above the main PCB 422 (so as not to
put strain on it) whilst transmitting data via the spring contacts
478 at the base of the packaged force sensor 500. The resulting
assembly fits neatly into the pen chassis molding 416 and is easy
to hand assemble.
Top/Side Loading Cartridge
[0301] As discussed above, the pen will require periodic
replacement of the ink cartridge during its lifetime. While the
front loading ink cartridge system is convenient for users, it can
have some disadvantages. Front loading limits the capacity of the
ink reservoir in the cartridge, since the diameter of the cartridge
along its full length is limited to the minimum cartridge diameter,
as dictated by the constraints of the pen nose.
[0302] The cartridge 414 must be pushed against the force sensor IC
526 (via the steel ball 524) by a pre-load spring 700 (see FIG.
33). However, the cartridge 414 itself does not provide the face
against which the spring pushes, since the cartridge must pass
through the spring. This necessitates the boot 702 or retaining
spring 504 discussed above. The boot is necessarily a compromise
between allowing easy manual insertion and removal of cartridge,
and ensuring the cartridge is held securely without travel.
[0303] A `top-loading` cartridge, as illustrated in FIG. 34, can
overcome these disadvantages. It will be appreciated that `top
loading` is a reference to insertion of the cartridge from a
direction transverse to the longitudinal axis of the pen. Because
of the other components within the pen, it is most convenient to
insert the cartridge from the `top` or apex 420 of the pen's
substantially triangular cross section (see FIG. 13).
[0304] The pre-load spring 700 can be placed toward the nib 418 of
the cartridge 414, thus providing a convenient mechanism for
seating the cartridge against the force sensor ball 524 after
insertion. A cartridge travel stop 712 is formed on the chassis
molding 416 to prevent overloading the force sensor 526. Since the
cartridge itself provides the face against which the pre-load
spring pushes, the boot is eliminated and the cartridge couples
directly with the force sensor.
[0305] As the cartridge is no longer constrained to a single
diameter along its full length, its central section can be wider
and accommodate a much larger ink reservoir 710.
[0306] The currently proposed pen design has an internal chassis
416 and an external tube molding 466. The external molding 466 is
user replaceable, allowing the user to customise the pen 400.
Removing the external molding 466 also provides the user with
access to the pen's product label 652 (see FIG. 71). Skilled
workers in this field will appreciate that the chassis molding 416
and the base molding 528 could be modified to provide the user with
access to a replaceable battery.
[0307] Referring again to FIG. 34, removing the external molding
466 (not shown) can also provide the user with access to the
top-loading pen cartridge 414. Once the external molding is
removed, most of the length of the pen cartridge 414 is exposed.
The user removes the cartridge by sliding it forwards against the
pre-load spring 700 to extract its tail 718 from the force sensor
aperture 720, then tilting it upwards to free the tail 718 from the
cartridge cavity 722, and finally withdrawing the cartridge 710
from the pre-load spring 700 and cavity 722. The user inserts a new
cartridge by following the same procedure in reverse.
[0308] Since a top-loading cartridge can have a much greater
capacity than a front-loading cartridge, it is not unreasonable to
require the user to remove the external molding 466 to replace the
cartridge 414, since the user will have to replace a top-loading
cartridge much less often than a front-loading cartridge.
[0309] Referring to FIG. 35, the pre-load spring 700 can be
provided with its own cavity 716 and retaining ring 714 to make it
easier to insert the cartridge 414.
Force Re-Directing Coupling
[0310] The force sensor 526 is ideally mounted perpendicularly to
the pen cartridge 414, as illustrated in FIG. 33. This allows
direct coupling between the pen cartridge and the force sensor.
This coupling is somewhat independent of whether there is an
intermediate boot 702 or not, as discussed above in relation to the
side loading cartridge. To fit within the constrained space of the
pen's tubular moulding 466, it can be advantageous to mount the
force sensor 526 in any desired position relative to the cartridge
414. This involves re-directing at least part of the contact force
being transferred along the cartridge 414.
[0311] A suitable force sensor 526 for the pen is a silicon
piezoresistive bridge force sensor, such as manufactured by
Hokuriku (see Hokuriku, Force Sensor HFD-500,
http://www.hdk.co.jp/pdf/eng/e1381AA.pdf for details). The
invention will be illustrated with reference to this force sensor.
However it will be appreciated that many other force sensors are
also suitable.
[0312] As shown in FIG. 36, the standard Hokuriku force sensor
package measures 5.2 mm wide by 7.0 mm long (or 8.0 mm with leads)
by about 3 mm thick. This thickness includes the ball 524, which
protrudes 150-200 microns. The headroom above the PCB 422 in the
embodiment shown is just over 5 mm. The pen cartridge axis extends
centrally through the boot 702 and is just under 3 mm above the PCB
422. It is therefore possible to mount the standard Hokuriku force
sensor package 526 on the PCB 422, either longitudinally (see FIGS.
37A and 37B) or possibly laterally (see FIG. 38), and provide an
off-axis coupling mechanism between the pen cartridge 418 and the
force sensor 526.
[0313] FIG. 36 shows a force transfer element in the form of a
double-bow coupling piece 726 between the cartridge 414 and the
force sensor 526. The lower, or force transfer bow 730 expands
downwards when subject to force from the cartridge via the boot
702. The force is transmitted through a right angle, providing the
required coupling between the cartridge 414 and the force sensor
526 mounted on the PCB 422. Each bow 728 and 730 is formed from a
flexible sheet. The edges of each sheet are curved to minimize
friction with the walls of the cavity.
[0314] The double-bow design acts as a centralizer, preventing the
cartridge 414 from moving upwards when force is applied, and
eliminating an area of friction. The top of the upper bow 728 can
be pinned, if necessary, to eliminate another point of friction (or
the cavity itself can provide a curved ridge contact). Friction
between the force transfer bow 730 and the ball 524 of the force
sensor 526 is small because the curvature of the ball minimizes the
contact area.
[0315] The force sensor 526 mates with a recess in the chassis
moulding 416 to form the cavity in which the double-bow coupling
piece 726 operates.
[0316] The pen cartridge 414 or the boot 702 necessarily engages
with the coupling piece 726 above the axis of the cartridge 414,
since it is impractical to align the two while efficiently
utilizing the available space. However, because the ratio of the
length of the cartridge to its diameter is large, negligible
torsion is induced by this off-axis coupling. As discussed above,
the centralizing function of the double-bow design minimizes
friction.
[0317] The double bow coupling piece 726 can be thought of as
having two spring constants. When unconstrained by the cavity, the
double bow can act as a reasonably soft spring. It should be soft
enough to guarantee that it expands to fill the cavity when
subjected to the force of the preload spring. The softness will
also be a function of the manufacturing tolerances of both the
cavity and the double-bow coupling piece 726. When the top bow 728
is constrained by the cavity, the double bow coupling piece 726 can
act as a very stiff spring. It should be stiff enough to avoid
resonant frequencies which overlap frequencies of interest in the
real force signal.
[0318] The force sensor 526 shown in FIGS. 20, 24 and 63A to 63E is
mounted in the chassis moulding 416, and makes electrical contact
with the PCB 422 via a set of sprung leads. This prevents force
being transmitted to solder joints between the force sensor 526 and
the PCB 422, and to the PCB itself.
[0319] By contrast, in this aspect of the invention, the force
sensor 526 is mounted flush with the PCB 422 and is therefore
ideally soldered to it. Furthermore, the force sensor 526 must be
securely attached to the chassis moulding 416 because it will be
subject to a force pushing it away from the moulding.
[0320] To make this practical, the PCB 422 can be securely attached
to the chassis moulding 416 via a set of clips formed in the
chassis moulding 416 and extending below the PCB 422. Pins can also
be provided as part of the chassis moulding 416, to penetrate and
anchor the PCB 422. The PCB 422 can then float within the tubular
body 466, with its main anchor point being in the centre of the
pen, at the location of the force sensor 526.
[0321] The embodiments shown in FIGS. 37A to 50, re-direct the
force (at least partially) from the cartridge or boot 702, to the
sensor 526, via a hydraulic coupling. As with the double bow
coupling, this allows the force sensor to be positioned
conveniently within the constraints of the pen body, and addresses
other problems such as damage from the deceleration shock when the
pen is tapped or dropped, and a relatively undamped transient
response which limits the available sensor bandwidth.
[0322] The general layout of the design is shown in FIGS. 37A, 37B
and 38 using the Hokuriku HFD-500 force sensor discussed above in
relation to the double bow coupling. As previously mentioned, other
high range pressure sensors are also suitable. The sensor 526 can
be used with or without the ball bearing 524. The PCB 422 needs to
float on its mounts so that the end stop behind the over-mould 734
brings all the axial pen force onto the pen chassis (not shown)
rather than the surface-mount connection to the PCB 422.
[0323] FIGS. 39A and 39B show the hydraulic coupling in more
detail. The ink cartridge 418 has a nib at its distal end and a
boot 702 at the opposite end. The boot pushes a plunger 732 onto a
membrane or gel surface 742 through an aperture in the over moulded
package 734. The increased pressure in the hydraulic fluid or gel
736 acts on the ball bearing 524 of the force sensor 526. The
output signal from the sensor 526 is transmitted directly to
contacts on the PCB 422 via pins 740.
[0324] The action of the input force F on the force sensor is
schematically shown in FIGS. 40 and 41. It will be appreciated that
these sketches are simplified and without the right-angle bend. The
right angle in the fluid path has no effect on the fluid at low
flow rates.
[0325] FIG. 40 represents the situation with an unmodified Hokuriku
sensor 526. The ball 524 acts as a piston, approximately, as its
cross-sectional area normal to the direction of travel hardly
changes.
[0326] Pressure throughout the fluid or gel 736, (in the case of
the Hokuriku sensor, silicone gel) is constant so: P=F/Ai=Fo/Ao,
[0327] Where P is the pressure in the gel; [0328] F is the input
force; [0329] Fo is sensed force; [0330] Ai is the area of the
plunger; [0331] Ao is the projected surface area of the ball in
plan view, or effective diaphragm size. [0332] Thus Fo/F=Ao/Ai
[0333] This ratio of the output force to the applied force is here
termed the Gearing Ratio (gr). Experimental results show that the
Gearing Ratio for the Hokuriku sensor is 0.22.
[0334] FIG. 41 shows the Hokuriku sensor having been modified to
remove the ball. The cavity of the sensor 526 is also filled with
the fluid or gel 736 and the pressure acts directly on the sensor
chip 526, so the effective diaphragm size (Ao) is the top surface
of the sensor chip 526.
[0335] The difference between using a sensor with the ball bearing
524 and without the ball bearing, is that the top surface of the
chip 526 does not act as a piston, but rather it deforms like a
balloon. The force sensor chip is actually sensing a pressure
instead of a force. Compare the typical force sensor deflection
profile in FIG. 42 to a typical pressure sensor deflection profile
in FIG. 43. The deflection in the pressure sensor case will be less
at the centre of the chip and it will be less sensitive, but
simpler. This diaphragm diameter is also different from the first
case and so will provide a different gearing ratio. A practical
realisation of the sensor configured to respond to the pressure in
the hydraulic coupling is shown in FIG. 44. It is important to vent
the cavity 748 beneath the force sensor chip 526 with an aperture
through the moulding 734.
[0336] Any sensor chip 526 responsive to differential pressure can
be used. However, high sensitivity are less preferred. The back of
the chip must be open to the ambient air pressure. The range of
pressures is in the order of atmospheres, so high-sensitivity
sensor chips are less suitable, eg. 500 g force over a 4 mm.sup.2
diaphragm (top surface of sensor chip) is 1.3 MPa=181 PSI=12
atm.
[0337] The fluid or gel 736 in the casing 734 should be
incompressible. All bubbles should be removed, with a vacuum if
necessary. The difference between various fluids is the sheer force
and the resulting pressure head (loss) and loss of transmitted
force. Fin(effective)=Fin-Fsheer Peffective=Fin(eff)/Ai-Phead
[0338] The pressure head loss is insignificant for silicone gel and
it has proven to be a suitable for the requirements of the force
sensor 526. However other fluids or gels may be used and the issues
to be considered when selecting a suitable fill for the casing are:
[0339] i Lower viscosity decreases the strength of the chip 526 (or
more correctly, the chip needs to be less rigid) and the easier it
is to break. [0340] ii Higher viscosity causes more hysteresis
loss. The sensor signal should return-to-zero setting after release
of the input force. [0341] iii Secondary effects (resonant
frequencies and standing waves) related to the effective elasticity
of the coupling fill should be minimised. [0342] iv Losses in the
high frequencies can help to dampen the step/impulse response.
[0343] The elasticity of the boot, mounting, and writing surface
all affect the self-resonant oscillations. A softer coupling (low
stiffiess) lowers the oscillation frequency, which is undesirable.
Conversely, a stiffer coupling increases the deceleration force
component of the pen-down action (for convenience, the pen down
response is referred to as the "F1" response). This F1 response
provides an unwanted artefact in the force signal and increases the
risk of chip breakage. FIG. 45 shows a typical tap response output
signal that illustrates the F1 response.
[0344] There are several possibilities for applying the input force
to the hydraulic fluid or gel 736. Three of the primary options are
shown in FIGS. 46A to 46C.
[0345] In FIG. 46A, the input piston 752 forms a sliding fit with
the aperture in the casing 734. The piston is overly complicated
for a microstructure and sealing the sides will cause
friction--which is highly undesirable.
[0346] In FIG. 46B, the input force F acts directly on an outwardly
bulging membrane 754. The diaphragm 754 is really only relevant to
pressure sensors where the input is a liquid or gas.
[0347] FIG. 46C shows a diaphragm 754 and plunger 752 combination.
This mechanism can be made robust so that it is difficult to burst,
the surface strength of the diaphragm 754 does not need to be so
high that it interferes with force transmission and the exhaust of
material around the sides of the plunger 752 can be restrained as
it lowers the spring constant of the coupling and reduce the
frequency response of the step/impulse function. Also, the
exhausted material and wall expansion of the casing 734 (see FIG.
41) increases the volume ratio (see N calculated below). Some
increase is tolerable and in fact might be desirable for protecting
the chip.
[0348] When designing the force input mechanism of FIG. 46C, the
relevant considerations are: [0349] i Shear force/piston effect
[0350] ii Strength: plunger collapses into the fluid [0351] iii Gap
provides a vent for the fluid to oscillate in and softens the
coupling--undesirably lowering the oscillation frequency (see
above). [0352] iv Gap magnifies the volume ratio of the input
piston relative to the output piston (perfect piston
behaviour).
[0353] Volume ratio: N=(Xin.times.Ain)/(Xout.times.Aout), where X
is the axial displacement,
[0354] N is approximately 20, if Xin at an input force of 500 g is
approximately 400 microns.
[0355] Up to a point this axial magnification (Xin/Xout) is good as
it means, in this case, that the 10 microns movement of the sensor
diaphragm 754 might give a 0.2 mm cartridge movement. This allows a
better end-stop protection mechanism (see FIG. 37B) to be used that
does not have such critical tolerance requirements.
[0356] The surface of the diaphragm 754 can be: [0357] i Just the
soft bulk material of the semi-cured silicone. [0358] ii Silicone
with a thin membrane [0359] iii Silicone with say an epoxy (etc)
painted over it. [0360] iv The outer part of the fluid would be
extra-hardened with a surface treatment. [0361] v A welded
film.
[0362] A thin membrane over silicone option is very fragile. The
welded film can be too strong and already pre-strained, so most of
the applied force is lost in stretching the film and not translated
into fluid pressure. The welded film configuration is shown in
FIGS. 47A to 47C. In FIG. 47A, the input force F.sub.i is lost to
F.sub.s used for stretching the film 756. In FIG. 47B, the film 756
initially bulges outwardly so that the plunger 752 acts to reduce
the film stretching and more of F.sub.i is used to raise the fluid
pressure. However, as shown in FIG. 47C, the film 756 bulges, or
exhausts around the sides of the plunger 752 when F.sub.i and
therefore plunger displacement, are relatively high. In this case,
considerations i to iv discussed above become relevant.
End Stop for Directly Coupled Sensor
[0363] If a force re-directing coupling is not used, and the sensor
is directly coupled to the cartridge or the boot (see FIG. 33), the
issue of overload damage to the sensor becomes a problem. The
Hokuriku chip (referred to above) breaks at a static deflection of
.about.50 microns at an applied force of 4.5 kg. Most of this
deflection is in the moulded casing 734, not the chip 526. For
example, at 500 g the 10 micron deflection is composed of no more
than 2 microns in the chip 526, the remaining 8 microns being in
the moulded casing.
Static Overload Protection
[0364] To protect the chip 526 from static overload an end-stop
that is set nominally at say 1 kg (equating to 16 microns
deflection) would have to engage the casing somewhere between at 10
microns and 21 microns. Fabricating an end-stop to this accuracy is
difficult. Firstly the end-stop has to be referenced with respect
to the back of the moulded casing 734, as the internal deflection
of the chip 526 relative to the package is small. Tests confirm
that an end-stop referenced to the front face does not protect the
chip 526 as effectively.
[0365] FIGS. 48 and 49 show end stop arrangements 738 referenced to
the back of the moulded casing. Testing has shown these
arrangements to be successful at protecting the chip at large
static loads without excessive interference in normal operation.
The flange 758 should engage the end-stop 738 at all points within
a very short range of travel of the boot 702. This complicates the
manufactures but an excessive engagement range can exceed the full
scale operating range of the sensor 526.
[0366] FIG. 49 is a more detailed sketch of the sensor and end stop
in the pen context. Contact pressure on the nib 418 is directly
transmitted up the cartridge 414 to the ball 524 of the sensor 526.
The end of the cartridge 414 is in the boot 702 which is pre-loaded
against the ball 524 by the pre-load spring 700. The end stop 738
takes the form of a cup-shaped element with a stop surface 712 at
its top for engagement with the boot 702. An optional layer 760 of
material with a known spring constant can be positioned behind the
sensor 526 for additional breakage protection.
Dynamic Load Protection
[0367] Shock loading is a problem for directly coupled force sensor
as well as fluid coupled sensors. The fluid or gel transmits the
deceleration shock just as well as the direct mechanical coupling.
However, the membranes in the fluid couplings tend to break rather
than the chips. Either failure would be irreparable in the Netpage
pen shown in the figures, as there are no serviceable parts other
than the removable cartridge and battery pack.
[0368] Fortunately, the "volume magnification" effect of the fluid
coupling helps because it magnifies the failure threshold
displacement.
[0369] As above: Xin/Xout=N.times.Aout/Ain=N.times.gr=displacement
magnification [0370] where: [0371] N=volume ratio [0372] gr=gearing
ratio [0373] assuming no secondary effects. [0374] So for the
displacement magnification=10 (say) Xin@500 g=10.times.10=100
microns
[0375] An end-stop fitted to prevent displacements of this
dimension is more easily manufactured than one configured to stop
10 micron displacements. From FIG. 50, the ordinary worker will
appreciate that a 100 micron gap between the flange 758 of the
plunger 732 and the stop surface 712 of the end stop 738 is far
easier than a 10 micron gap.
Deformable Force Sensor Coupling
[0376] For direct coupling between the pen cartridge (or boot) and
the force sensor, the sensor is mounted so that the plane of the
chip 526 is perpendicular to the axis of the cartridge 414 (see
FIG. 33). This coupling is somewhat independent of whether the
assembly includes the boot 702 over the end of the cartridge
414.
[0377] The force sensor 526 deflects in response to an applied
force F. As discussed above, the sensor may break when the applied
force exceeds the elastic limits of the sensor.
[0378] As shown in FIG. 33, the force sensor 526 may be recessed to
prevent excessive deflection. However, even if the force sensor is
protected from an excessive static force, an impulse may still be
sufficient to break the sensor, such as when the pen is dropped on
its nib 418.
[0379] To prevent an impulse from breaking the force sensor, an
element may be inserted between the nib and the force sensor that
can collapse or grossly deform when the input force is above a safe
threshold. The collapsible element is designed to absorb the energy
of an impulse originating at the nib by collapsing, thus preventing
the impulse from propagating to the force sensor.
[0380] The collapsible element may be designed to collapse
permanently or temporarily.
[0381] If the collapsible element is designed to collapse
permanently, then it is most usefully incorporated into the
cartridge, since the cartridge is already designed to be
replaceable by the user when the ink supply is exhausted or the nib
is damaged.
[0382] FIG. 51 shows a pen cartridge 414 with an integral
collapsible element 766. The collapsible element 766 consists of a
set of struts 770 joining two parts 762 and 764 of the cartridge
414. The struts 770 transmit axial forces throughout the full
dynamic range of the force sensor without substantial deformation,
but are designed to have a buckling threshold, as shown in FIG. 52,
when exposed to an excessive force or damaging impulse F. The outer
section 764 of the cartridge 414 is permanently displaced along the
longitudinal axis 768 toward the inner section 762 proximate the
force sensor. To assist crumpling the struts 770 are set at an
angle to the axis of the cartridge.
[0383] The example shows two struts, but additional struts can be
used.
[0384] In a felt-tip pen cartridge or similar, the nib 418 itself
can be used as the collapsible element. In a ballpoint pen
cartridge 414 the housing surrounding the nib 418 can also be used
as the collapsible element 766.
[0385] FIG. 53 shows a temporarily collapsible element 766 suitable
for insertion between the pen cartridge 414 and the force sensor.
The collapsible element 766 consists of a pair of rods 762 and 764
held in an elastomeric sleeve 772, with both rods meeting at a slip
surface 776 inclined to the longitudinal axis 768.
[0386] The element 766 transmits axial forces throughout the full
dynamic range of the force sensor without slipping, but is designed
to slip, as shown in FIG. 54, when exposed to an excessive force or
damaging impulse F. The stick friction at the slip surface 776 and
the force of the elastomeric sleeve 772 keeps the rods 762 and 764
from slipping except when exposed to an excessive force.
[0387] When the excessive force is removed the elastomeric sleeve
772 aligns the rods to restore the un-collapsed state of the
collapsible element. Locating features 774 on both rods 762 and 764
prevent the sleeve 772 from moving away from the slip surface
776.
[0388] FIG. 55 is a sectioned perspective of the stick friction
collapsible element 766, and shows the elastomeric sleeve 772
surrounding the mated rods 762 and 764.
Optical Force Sensor
[0389] The Hokuriku force sensor discussed above is piezoresistive.
Sensors of this type present several challenges. They necessitate a
precision-assembly and the required form factor is not currently
available in a standard part. Hence to prototype the part and tool
up for volume production is costly. Furthermore, its full-force
deflection is small, requiring careful tolerancing to prevent
breakage.
[0390] To avoid these problems, this aspect of the invention
provides an optical force sensor that uses the attenuation of an
optical coupling between a light-emitting diode (LED) and a
photodetector.
[0391] FIG. 33 shows a typical configuration of a force sensor 526
coupled with a pen cartridge 414 within a pen body 416. The
cartridge 414 is pre-loaded (spring 700) against the force sensor
to eliminate travel before force sensing commences and to eliminate
the need for fine tolerancing of the coupling between the force
sensor and the cartridge (or the boot 702 which grips the cartridge
414).
[0392] FIGS. 56A and 56B shows the optical force sensor. It
consists of a rigid but movable core held within a rigid housing
416. The end of the housing 416 has an opening (on the left)
through which the end of the core 786 protrudes and engages with
the pen cartridge (or boot) as shown in FIG. 33. The other end of
the core engages with a spring 784.
[0393] The other end of the housing 416 also has an opening (on the
right) through which the other end of the core 786 protrudes to
ensure the core remains centred in the housing.
[0394] The centre of the core has an aperture 782 which faces a LED
780 on one side and a photodetector 778 on the other.
[0395] As the cartridge 414 pushes against the core 786, the core
786 pushes against the spring 784 and compresses it in proportion
to the force applied to the cartridge 414. As the core 786 moves in
proportion to the applied force, the aperture 782 moves relative to
the LED 780 and photodetector 778. The amount of light detected by
the photodetector 778 is therefore a function of the position of
the core 786 and hence of the applied force.
[0396] The shape of the aperture 782 and the shape of the housing
surrounding the LED 780 and the photodetector 778 determine how
much light strikes the photodetector 778 as a function of the
position of the core 782. The amount of light is also affected by
the beam profile of the LED, and this can be modified by using a
collimating lens or a diffuser in front of the LED.
[0397] The force sensor has a desired dynamic range. The aperture
782 is positioned relative to the LED 780 and photodetector 778 so
that when zero external force is applied close to zero light
strikes the photodetector 778. The spring 784 is chosen so that
when maximum external force is applied the core 786 is displaced so
that the aperture 782 aligns with the LED 780 and photodetector 778
and maximum light strikes the photodetector 778. The aperture 782
is made wide enough so that transverse movement of the core 786 in
the housing 416 does not affect light transmission.
[0398] If the maximum external force is F.sub.max and the length of
the aperture is a, then the required stiffness k of the spring is:
k=F.sub.max/a (EQ 1)
[0399] During use of the pen, axial cartridge movement up to 100
microns is acceptable, and this imposes an upper limit on the
length of the aperture. Although this would seem to impose severe
mechanical tolerancing requirements on the length of the movable
core, the length of the chamber which houses the core, and the
length of the spring, this is not necessarily so. When the force
sensor is assembled, the core does not need to be in contact with
the spring. Instead, the external spring which pre-loads the pen
cartridge against the force sensor can also be relied upon to
pre-load the core against the force sensor spring. However, the
aperture in the core has to be long enough to accommodate the full
range of movement of the core.
[0400] The force is sampled at a rate that is determined by the
expected frequency content of the force signal, the maximum allowed
latency in detecting pen-down and pen-up events, and any
requirement to low-pass filter the force signal to remove
noise.
[0401] FIG. 57 shows a high-level block diagram of the force
sensor. A force sensor controller 582 uses a pulse-width modulator
(PWM) 788 to drive the LED 780 with a desired intensity. It uses an
analog-to-digital converter (ADC) 790 to sample the photodetector
(PD) 778 signal which represents the force signal. The PD 778
output current is converted to a voltage before being sampled by
the ADC 790. It is amplified by a programmable-gain amplifier (PGA)
792 and is typically also low-pass filtered.
[0402] The force sensor controller 582 can use the PWM 788 to cycle
the LED 780 through a set of different intensities, and combine
successive ADC 790 samples to obtain a higher-precision signal. In
the limit case the ADC 790 can be a simple comparator.
[0403] The force sensor controller 582 can also operate in multiple
modes. For example, when in pen-up mode it can simply be looking
for a pen-down transition, while in pen-down mode it can be
sampling the force signal with higher precision. A simple pen-down
detection mode can help minimise power consumption.
[0404] The force sensor can be calibrated in the factory to
determine the transfer function from applied force to photodetector
output, and this can be used to determine gain and offset settings
for the PGA 792. The force sensor can also measure its zero-force
signal when capped, and utilise an otherwise fixed transfer
function.
Force Sensor Dilatant Fluid Stop
[0405] As previously discussed, direct coupling between the pen
cartridge (or boot) and the force sensor, requires the sensor to be
mounted so that the plane of the chip 526 is perpendicular to the
axis of the cartridge 414 (see FIG. 33). This coupling is somewhat
independent of whether the assembly includes the boot 702 over the
end of the cartridge 414.
[0406] The force sensor 526 deflects in response to an applied
force F. As discussed above, the sensor may break when the applied
force exceeds the elastic limits of the sensor.
[0407] As shown in FIG. 33, the force sensor 526 may be recessed to
prevent excessive deflection. However, even if the force sensor is
protected from an excessive static force, an impulse may still be
sufficient to break the sensor, such as when the pen is dropped on
its nib 418.
[0408] A dilatant (or "shear thickening") fluid is a non-Newtonian
fluid whose viscosity increases with rate of shear. Dilatant fluids
are typically dispersions of solid particles in a liquid at a
critical particle concentration which allows the particles to
touch. At a low shear rate the particles are able to slide past
each other and the fluid behaves as a liquid. Above a critical
shear rate friction between the particles predominates and the
fluid behaves as a solid. Although the best-known dilatant fluid
consists of a cornstarch dispersion in water, industrial dilatant
fluids typically consist of polymer dispersions in alcohol or water
(see for example U.S. Pat. No. 5,037,880 to Schmidt et al).
[0409] To prevent damage to the force sensor 526 from an impulse,
an additional stop 798 containing a dilatant fluid 796 can be
inserted between the boot 702 (or cartridge 414) and the force
sensor 526, as shown in FIG. 58. The dilatant fluid 796 can be
contained in a sack 798 with a flexible membrane, formed into an
o-ring to allow direct contact between the boot 702 (or cartridge)
and the force sensor 526 through the hole in the middle.
[0410] During normal operation of the pen, the dilatant fluid
o-ring acts as a liquid and deforms in response to movement of the
cartridge 414, allowing normal forces to be transmitted from the
cartridge to the force sensor 526. When a damaging impulse occurs,
the dilatant fluid o-ring effectively hardens in response to the
high shear rate, preventing movement of the cartridge and thereby
protecting the force sensor.
[0411] The thickness of the o-ring does not need to be finely
toleranced because the preload spring 700 preloads the cartridge
414 against the force sensor 526 largely independently of the
o-ring. However, the ball 524 of the force sensor 526 needs to be
sufficiently proud of the force sensor recess, formed by the
surrounding stop 712, to accommodate at least some dilatant fluid
796 between the boot 702 and the stop 712 when the force sensor is
preloaded.
[0412] If the boot is provided with a pin 718, as shown in FIG. 59,
then a thicker o-ring can be accommodated. There is more
displacement of the cartridge during a normal pen down event, but a
thicker o-ring affords greater protection for the sensor 526.
Cap Assembly
[0413] The pen cap assembly 472 consists of four moldings as shown
in FIG. 25. These moldings combine to produce a pen cap which can
be stowed on the top end of the pen 456 during operation. When
capped, it provides a switch to the electronics to signal the
capped state (described in `Cap Detection Circuit` section below).
A conductive elastomeric molding 522 inside the cap 410 functions
as the cap switch when it connects the inner 512 and outer 514
metal tubes to short circuit them (see FIG. 26). The conductive
elastomeric molding 522 is pushed into a base recess in the cap
molding 410. It is held captive by the clip molding 544 which is
offered into the cap and snaps in place. A metallised trim molding
546 snaps onto the cap molding 410 to complete the assembly
472.
[0414] The cap molding 410 is line-of-draw and has an aquagraphic
print applied to it. The trim 546 can be metallised in reflective
silver or gold type finishes as well as coloured plastics if
required.
Pen Feedback Systems--Vibratory
[0415] The pen 400 has two sensory feedback systems. The first
system is haptic, in the form of a vibration motor 446. In most
instances this is the primary user feedback system as it is in
direct contact with the users hand 408 and the `shaking` can be
instantly felt and not ignored or missed.
Pen Feedback Systems--Visual
[0416] The second system is a visual indication in the form of an
indicator window 412 in the tube molding 466 on the top apex 420 of
the pen 400. This window aligns with a light pipe 448 in the
chassis molding 416, which transmits light from red and green
indicator LEDs 452 on the main PCB 422. The indicator window 412 is
positioned so that it is not covered by the user's hand 408 and it
is also unobstructed when the cap 410 is stowed on the top end 456
of the pen.
Optical Design
[0417] The pen incorporates a fixed-focus narrowband infrared
imaging system. It utilises a camera with a short exposure time,
small aperture, and bright synchronised illumination to capture
sharp images unaffected by defocus blur or motion blur.
TABLE-US-00005 TABLE 5 Optical Specifications Magnification -0.225
Focal length of lens 6.0 mm Viewing distance 30.5 mm Total track
length 41.0 mm Aperture diameter 0.8 mm Depth of field +/-6.5
mm.sup.7 Exposure time 200 us Wavelength 810 nm.sup.8 Image sensor
size 140 .times. 140 pixels Pixel size 10 um Pitch range.sup.9 -15
to +45 deg Roll range -30 to +30 deg Yaw range 0 to 360 deg Minimum
sampling 2.25 pixels per rate macrodot Maximum pen velocity 0.5 m/s
.sup.7Allowing 70 um blur radius .sup.8Illumination and filter
.sup.9Pitch, roll and yaw are relative to the axis of the pen.
Pen Optics and Design Overview
[0418] Cross sections showing the pen optics are provided in FIGS.
27A and 27B. An image of the Netpage tags printed on a surface 548
adjacent to the nib 418 is focused by a lens 488 onto the active
region of an image sensor 490. A small aperture 494 ensures the
available depth of field accommodates the required pitch and roll
ranges of the pen 400.
[0419] First and second LEDs 434 and 436 brightly illuminate the
surface 549 within the field of view 430. The spectral emission
peak of the LEDs is matched to the spectral absorption peak of the
infrared ink used to print Netpage tags to maximise contrast in
captured images of tags. The brightness of the LEDs is matched to
the small aperture size and short exposure time required to
minimise defocus and motion blur.
[0420] A longpass IR filter 432 suppresses the response of the
image sensor 490 to any coloured graphics or text spatially
coincident with imaged tags and any ambient illumination below the
cut-off wavelength of the filter 432. The transmission of the
filter 432 is matched to the spectral absorption peak of the
infrared ink to maximise contrast in captured images of tags. The
filter also acts as a robust physical window, preventing
contaminants from entering the optical assembly 470.
The Imaging System
[0421] A ray trace of the optic path is shown in FIG. 28. The image
sensor 490 is a CMOS image sensor with an active region of 140
pixels squared. Each pixel is 10 .mu.m squared, with a fill factor
of 93%. Turning to FIG. 29, the lens 488 is shown in detail. The
dimensions are: [0422] D=3 mm [0423] R1=3.593 mm [0424] R2=15.0 mm
[0425] X=0.8246 mm [0426] Y=1.0 mm [0427] Z=0.25 mm
[0428] This gives a focal length of 6.15 mm and transfers the image
from the object plane (tagged surface 548) to the image plane
(image sensor 490) with the correct sampling frequency to
successfiilly decode all images over the specified pitch, roll and
yaw ranges. The lens 488 is biconvex, with the most curved surface
facing the image sensor. The minimum imaging field of view 430
required to guarantee acquisition of an entire tag has a diameter
of 39.6s (s=spacing between macrodots in the tag pattern) allowing
for arbitrary alignment between the surface coding and the field of
view. Given a macrodot spacing, s, of 143 .mu.m, this gives a
required field of view of 5.7 mm.
[0429] The required paraxial magnification of the optical system is
defined by the minimum spatial sampling frequency of 2.25 pixels
per macrodot for the fully specified tilt range of the pen 400, for
the image sensor 490 of 10 .mu.m pixels. Thus, the imaging system
employs a paraxial magnification of -0.225, the ratio of the
diameter of the inverted image (1.28 mm) at the image sensor to the
diameter of the field of view (5.7 mm) at the object plane, on an
image sensor 490 of minimum 128.times.128 pixels. The image sensor
490 however is 140.times.140 pixels, in order to accommodate
manufacturing tolerances. This allows up to +/-120 .mu.m (12 pixels
in each direction in the plane of the image sensor) of misalignment
between the optical axis and the image sensor axis without losing
any of the information in the field of view.
[0430] The lens 488 is made from Poly-methyl-methacrylate (PMMA),
typically used for injection moulded optical components. PMMA is
scratch resistant, and has a refractive index of 1.49, with 90%
transmission at 810 nm. The lens is biconvex to assist moulding
precision and features a mounting surface to precisely mate the
lens with the optical barrel molding 492.
[0431] A 0.8 mm diameter aperture 494 is used to provide the depth
of field requirements of the design.
[0432] The specified tilt range of the pen is -15.0 to +45.0 degree
pitch, with a roll range of -30.0 to +30.0 the pen through its
specified range moves the tilted object plane up to 6.3 mm away
from the focal plane. The specified aperture thus provides a
corresponding depth of field of +/-6.5 mm, with an acceptable blur
radius at the image sensor of 16 .mu.m.
[0433] Due to the geometry of the pen design, the pen operates
correctly over a pitch range of -33.0 to +45.0 degrees. Referring
to FIG. 30, the optical axis 550 is pitched 0.8 degrees away from
the nib axis 552. The optical axis and the nib axis converge toward
the paper surface 548. With the nib axis 552 perpendicular to the
paper, the distance A between the edge of the field of view 430
closest to the nib axis and the nib axis itself is 1.2 mm.
[0434] The longpass IR filter 432 is made of CR-39, a lightweight
thermoset plastic heavily resistant to abrasion and chemicals such
as acetone. Because of these properties, the filter also serves as
a window. The filter is 1.5 mm thick, with a refractive index of
1.50. Each filter may be easily cut from a large sheet using a
CO.sub.2 laser cutter.
The Illumination System
[0435] The tagged surface 548 is illuminated by a pair of 3 mm
diameter LEDs 434 and 436. The LEDs emit 810 nm radiation with a
divergence half intensity, half angle of +/-15 degrees in a 35 nm
spectral band (FWHM), each with a power of approximately 45 mW per
steradian.
Pod Design and Assembly
[0436] TABLE-US-00006 TABLE 2 Pod Mechanical Specifications Size
h63 .times. w43 .times. d46 mm Mass 50 g Operating -10.about.+55 C
Temperature Operating Relative 10-90% Humidity Storage -20 to +60 C
worst case Temperature Storage Relative 5-95% Humidity Shock and
Vibration Drop from 1 m onto a hard surface without damage.
Mechanical shock 600 G, 2.5 ms, 6 axis. Serviceability Replaceable
jacket (part of customisation kit). No internal user serviceable
parts - the case is not user openable. Power USB: 500 mA. External
power adapter: 600 mA at 5.5 VDC.
Pod Design
[0437] The pen 400 is supplied with a USB tethered pod, which
provides power to the pen and a Bluetooth transceiver for data
transfer between the pen and the pod. Referring to FIG. 31, the pod
450 is a modular design and is comprised of several line of draw
moldings. The pod tower molding 554 holds the pen at a 15 degree
from vertical angle, which is both ergonomic from a pen stowing and
extraction perspective, but also is inherently stable.
Pod Assembly
[0438] The assembly sequence for the pod 450 is as follows:
[0439] An elastomeric stop molding 556 is push fitted into the pod
tower molding 554 to provide a positive stop for the pen when
inserted into the pod.
[0440] The pod tower molding 554 has two metal contacts 516 pushed
onto location ribs under the stop. These contacts 516 protrude into
a void 558 where the nib molding 428 is seated as shown in FIG. 32.
When a pen is present, they contact the coaxial metal barrels 498
around the ink cartridge 414. These act as conductors to provide
charge to the battery 424.
[0441] The pod PCB 560 is offered up into the pod tower molding 554
and snapped into place. Sprung charging contacts 562 on the metal
contact piece 516 align with power pads on the pod PCB 560 during
assembly. The underside of the pod PCB 450 includes several arrays
of red, green and blue LEDs 564 which indicate several charging
states from empty to full. Blue is the default `charging` and `pod
empty` status color and they are transmitted via a translucent
elastomeric light pipe 566 as an illuminated arc around the pod
base molding 568.
[0442] Despite a reasonable centre of gravity with a pen inserted,
a cast weight 570 sits in the base molding 568 to increase
stability and lessen the chance of the pod 450 falling over when
knocked. The base molding 568 screws into the tower molding 554 to
hold the weight 570, light pipe 566 and PCB 560 after the tethered
USB/power cable 572 is connected to the pod PCB 560.
Personalisation
[0443] In line with the market differentiation ability of the pen,
the pod includes a pod jacket molding 468. This user removable
molding is printed with the same aquagrahic transfer pattern as the
tube and cap moldings of the pen it is supplied with as a kit.
[0444] Therefore the pattern of the pen, cap and pod are three
items that strongly identify an individual users pen and pod to
avoid confusion where there are multiple products in the same
environment. They also allow this product to become a personal
statement for the user.
[0445] The pod jacket molding 468 can be supplied as an aftermarket
accessory in any number of patterns and images with the cap
assembly 472 and the tube molding 466 as discussed earlier.
Electronics Design
[0446] TABLE-US-00007 TABLE 3 Electrical Specifications Processor
ARM7 (Atmel AT91FR40162) running at 80 MHz with 256 kB SRAM and 2
MB flash memory Digital ink storage 5 hours of writing capacity
Bluetooth Compliance 1.2 USB Compliance 1.1 Battery standby time 12
hours (cap off), >4 weeks (cap on) Battery writing time 4 hours
of cursive writing (81% pen down, assuming easy offload of digital
ink) Battery charging time 2 hours Battery Life Typically 300
charging cycles or 2 years (whichever occurs first) to 80% of
initial capacity. Battery Capacity/Type .about.340 mAh at 3.7 V,
Lithium-ion Polymer (LiPo)
Pen Electronics Block Diagram
[0447] FIG. 60 is a block diagram of the pen electronics. The
electronics design for the pen is based around five main sections.
These are: [0448] the main ARM7 microprocessor 574, [0449] the
image sensor and image processor 576, [0450] the Bluetooth
communications module 578, [0451] the power management unit IC
(PMU) 580 and [0452] the force sensor microprocessor 582. ARM7
Microprocessor
[0453] The pen uses an Atmel AT91FR40162 microprocessor (see Atmel,
AT91ARM Thumb Microcontrollers--AT91FR40162 Preliminary,
http://www.keil.com/dd/docs/datashts/atmel/at91fr40162.pdf) running
at 80 MHz. The AT91FR40162 incorporates an ARM7 microprocessor, 256
kBytes of on-chip single wait state SRAM and 2 MBytes of external
flash memory in a stack chip package.
[0454] This microprocessor 574 forms the core of the pen 400. Its
duties include: [0455] setting up the Jupiter image sensor 584,
[0456] decoding images of Netpage coded impressions, with
assistance from the image processing features of the image sensor
584, for inclusion in the digital ink stream along with force
sensor data received from the force sensor microprocessor 582,
[0457] setting up the power management IC (PMU) 580, [0458]
compressing and sending digital ink via the Bluetooth
communications module 578, and [0459] programming the force sensor
microprocessor 582.
[0460] The ARM7 microprocessor 574 runs from an 80 MHz oscillator.
It communicates with the Jupiter image sensor 576 using a Universal
Synchronous Receiver Transmitter (USRT) 586 with a 40 MHz clock.
The ARM7 574 communicates with the Bluetooth module 578 using a
Universal Asynchronous Receiver Transmitter (UART) 588 running at
115.2 kbaud. Communications to the PMU 580 and the Force Sensor
microProcessor (FSP) 582 are performed using a Low Speed Serial bus
(LSS) 590. The LSS is implemented in software and uses two of the
microprocessor's general purpose IOs.
[0461] The ARM7 microprocessor 574 is programmed via its JTAG port.
This is done when the microprocessor is on the main PCB 422 by
probing bare pads 592 (see FIG. 63) on the PCB.
Jupiter Image Sensor
[0462] The Jupiter Image Sensor 584 (see U.S. Ser. No. 10/778,056
(Docket Number NPS047) listed in the cross referenced documents
above) contains a monochrome sensor array, an analogue to digital
converter (ADC), a frame store buffer, a simple image processor and
a phase lock loop (PLL). In the pen, Jupiter uses the USRT's clock
line and its internal PLL to generate all its clocking
requirements. Images captured by the sensor array are stored in the
frame store buffer. These images are decoded by the ARM7
microprocessor 574 with help from the Callisto image processor
contained in Jupiter.
[0463] Jupiter controls the strobing of two infrared LEDs 434 and
436 at the same time as its image array is exposed. One or other of
these two infrared LEDs may be turned off while the image array is
exposed to prevent specular reflection off the paper that can occur
at certain angles.
Bluetooth Communications Module
[0464] The pen uses a CSR BlueCore4-External device (see CSR,
BlueCore4-External Data Sheet rev c, Sep. 6, 2004) as the Bluetooth
controller 578. It requires an external 8 Mbit flash memory device
594 to hold its program code. The BlueCore4 meets the Bluetooth
v1.2 specification and is compliant to v0.9 of the Enhanced Data
Rate (EDR) specification which allows communication at up to 3
Mbps.
[0465] A 2.45 GHz chip antenna 486 is used on the pen for the
Bluetooth communications.
[0466] The BlueCore4 is capable of forming a UART to USB bridge.
This is used to allow USB communications via data/power socket 458
at the top of the pen 456.
[0467] Alternatives to Bluetooth include wireless LAN and PAN
standards such as IEEE 802.11 (Wi-Fi) (see IEEE, 802.11 Wireless
Local Area Networks,
http://grouper.ieee.org/groups/802/11/index.html), IEEE 802.15 (see
IEEE, 802.15 Working Group for WPAN,
http://grouper.ieee.org/groups/802/15/index.html), ZigBee (see
ZigBee Alliance, http://www.zigbee.org), and WirelessUSB Cypress
(see Wireless USB LR 2.4-GHz DSSS Radio SoC,
http://www.cypress.com/cfuploads/img/products/cywusb6935.pdf), as
well as mobile standards such as GSM (see GSM Association,
http://www.gsmworld.com/index.shtml), GPRS/EDGE, GPRS Platform,
http://www.gsmworld.com/technology/gprs/index.shtml), CDMA (see
CDMA Development Group, http://www.cdg.org/, and Qualcomm,
http://www.qualcomm.com), and UMTS (see 3rd Generation Partnership
Project (3GPP), http://www.3gpp.org).
Power Management Chip
[0468] The pen uses an Austria Microsystems AS3603 PMU 580 (see
Austria Microsystems, AS3603 Multi-Standard Power Management Unit
Data Sheet v2.0). The PMU is used for battery management, voltage
generation, power up reset generation and driving indicator LEDs
and the vibrator motor.
[0469] The PMU 580 communicates with the ARM7 microprocessor 574
via the LSS bus 590.
[0470] The PMU uses one of two sources for charging the battery
424. These are the power from the power and USB jack 458 at the top
of the pen 456 (see FIG. 15) and the power from the pod 450 via the
two conductive tubes 498 (see FIG. 24). The PMU charges the pen's
lithium polymer battery 424 using trickle current, constant current
and constant voltage modes with little intervention required by the
ARM7 microprocessor 574. The PMU also includes a fuel gauge which
is used by the ARM7 microprocessor to determine how much battery
capacity is left.
[0471] The PMU 580 generates the following separate voltages:
[0472] 3.0V from an LDO for the ARM7 IO voltage and the Jupiter IO
and pixel voltages. [0473] 3.0V from an LDO for the force sensor
and force sensor filter and amplifier (3.0V for the force sensor
microprocessor is generated from an off chip LDO since the PMU
contains no LDOs that can be left powered on). [0474] 3.0V from an
LDO for the BlueCore4 Bluetooth device. [0475] 1.8V from a buck
converter for the ARM7 core voltage. [0476] 1.85V from an LDO for
the Jupiter core voltage. [0477] 5.2V from a charge pump for the
infrared LED drive voltage.
[0478] At power up or reset of the PMU, the ARM7 IO voltage and
1.8V core voltage are available. The other voltage sources need to
be powered on via commands from the ARM7 574 via the LSS bus
590.
[0479] Indicator LEDs 444 and the vibrator motor 446 are driven
from current sink outputs of the PMU 580.
[0480] The PMU 580 can be put into ultra low power mode via a
command over the LSS bus 590. This powers down all of its external
voltage sources. The pen enters this ultra low power mode when its
cap assembly 472 is on.
[0481] When the cap 472 is removed or there is an RTC wake-up
alarm, the PMU 580 receives a power on signal 596 from the force
sensor microprocessor 582 and initiates a reset cycle. This holds
the ARM7 microprocessor 574 in a reset state until all voltages are
stable. A reset cycle can also be initiated by the ARM7 574 via a
LSS bus message or by a reset switch 598 which is located at the
top of the pen next to the USB and power jack 458 (see FIG.
15).
Force Sensor Subsystem
[0482] The force sensor subsystem comprises a custom Hokuriku force
sensor 500 (based on Hokuriku, HFD-500 Force Sensor,
http://www.hdk.co.jp/pdf/eng/e1381AA.pdf), an amplifier and low
pass filter 600 implemented using op-amps and a force sensor
microprocessor 582.
[0483] The pen uses a Silicon Laboratories C8051F330 as the force
sensor microprocessor 582 (see Silicon Laboratories, C8051F330/1
MCUData Sheet, rev 1.1). The C8051F330 is an 8051 microprocessor
with on chip flash memory, 10 bit ADC and 10 bit DAC. It contains
an internal 24.5 MHz oscillator and also uses an external 32.768
kHz tuning fork.
[0484] The Hokuriku force sensor 500 is a silicon piezoresistive
bridge sensor. An op-amp stage 600 amplifies and low pass
(anti-alias) filters the force sensor output. This signal is then
sampled by the force sensor microprocessor 582 at 5 kHz.
[0485] Alternatives to piezoresistive force sensing include
capacitive and inductive force sensing (see Wacom, "Variable
capacity condenser and pointer", US Patent Application 20010038384,
filed 8 Nov. 2001, and Wacom, Technology,
http://www.wacom-components.com/english/tech.asp).
[0486] The force sensor microprocessor 582 performs further
(digital) filtering of the force signal and produces the force
sensor values for the digital ink stream. A frame sync signal from
the Jupiter image sensor 576 is used to trigger the generation of
each force sample for the digital ink stream. The temperature is
measured via the force sensor microprocessor's 582 on chip
temperature sensor and this is used to compensate for the
temperature dependence of the force sensor and amplifier. The
offset of the force signal is dynamically controlled by input of
the microprocessor's DAC output into the amplifier stage 600.
[0487] The force sensor microprocessor 582 communicates with the
ARM7 microprocessor 574 via the LSS bus 590. There are two separate
interrupt lines from the force sensor microprocessor 582 to the
ARM7 microprocessor 574. One is used to indicate that a force
sensor sample is ready for reading and the other to indicate that a
pen down/up event has occurred.
[0488] The force sensor microprocessor flash memory is programmed
in-circuit by the ARM7 microprocessor 574. The force sensor
microprocessor 582 also provides the real time clock functionality
for the pen 400. The RTC function is performed in one of the
microprocessor's counter timers and runs from the external 32.768
kHz tuning fork. As a result, the force sensor microprocessor needs
to remain on when the cap 472 is on and the ARM7 574 is powered
down. Hence the force sensor microprocessor 582 uses a low power
LDO separate from the PMU 580 as its power source. The real time
clock functionality includes an interrupt which can be programmed
to power up the ARM7 574.
[0489] The cap switch 602 is monitored by the force sensor
microprocessor 582. When the cap assembly 472 is taken off (or
there is a real time clock interrupt), the force sensor
microprocessor 582 starts up the ARM7 572 by initiating a power on
and reset cycle in the PMU 580.
Pen Design
Electronics PCBs and Cables
[0490] There are two PCBs in the pen, the main PCB 422 (FIG. 63)
and the flex PCB 496 (FIG. 19). The other separate components in
the design are the battery 424, the force sensor 500, the vibrator
motor 446 and the conductive tubes 498 (FIG. 16) which function as
the power connector to the pod 450 (FIG. 31).
Main PCB
[0491] FIGS. 63 and 64 show top and bottom perspectives
respectively of the main PCB 422. The main PCB 422 is a 4-layer FR4
1.0 mm thick PCB with minimum trace width and separation of 100
microns. Via specification is 0.2 mm hole size in a 0.4 mm pad. The
main PCB 422 is a rectangular board with dimensions 105 mm.times.11
mm.
[0492] The major components which are soldered to the main PCB are
the Atmel ARM7 microprocessor 574, the AMS PMU 580, the Silicon
Labs force sensor microprocessor 582, the op-amps for force sensor
conditioning amplifier 600 and the CSR Bluetooth chip 578 and its
flash memory 594, antenna 486 and shielding can 612.
[0493] The force sensor 500, the vibrator motor 446 and the coaxial
conductive tubes 498 use sprung contacts to connect to pads on the
main PCB 422. All of these items are pushed down onto the main PCB
422 by the chassis molding 416 of the pen.
[0494] There are three connectors soldered onto the main PCB 422;
the flex PCB connector 612, the power and USB jack 458 at the top
of the pen 456, and the battery cable harness connector 616. The
cable harness to the battery is the only wired cable inside the
pen.
[0495] Also soldered onto the main PCB 422 is the reset switch 598.
This is in the recess 464 shown in FIG. 5.
Flex PCB
[0496] The Jupiter image sensor 576 is mounted on the flex PCB 496
as shown in FIG. 19. As the critical positioning tolerance in the
pen is between the optics 426 and the image sensor 490, the flex
PCB 496 allows the optical barrel molding 492 to be easily aligned
to the image sensor 490. By having a flexible connection between
the image sensor and the main PCB 422, the positioning tolerance of
the main PCB is not critical for the correct alignment of the
optics 426.
[0497] The image sensor 490, the two infrared LEDs 434 and 436, and
five discrete bypass capacitors 502 are mounted onto the flex PCB
496. The flex is a 2-layer polyimide PCB, nominally 75 microns
thick The PCB is specified as flex on install only, as,it is not
required to move after assembly of the pen. Stiffener 612 is placed
behind the discrete components 502 and behind the image sensor 490
in order to keep these sections of the PCB flat. Stiffener is also
placed at the connection pads 620 to make it the correct thickness
for the connector 614 the main PCB 422 (see FIG. 28). The PCB
design has been optimised for panel layout during manufacture by
keeping it roughly rectangular in overall shape.
[0498] The flex PCB 496 extends from the main PCB, widening around
the image sensor 490 and then has two arms 622 and 624 that travel
alongside the optical barrel 492 to the two infrared LEDs 434 and
436. These are soldered directly onto the arms 622 and 624 of flex
PCB. The total length of the flex PCB is 41.5 mm and at its widest
point it is 9.5 mm.
[0499] The image sensor 490 is mounted onto the flex PCB 496 using
a chip on flex PCB (COF) approach. In this technology, the bare
Jupiter die 628 is glued onto the flex PCB 496 and the pads on the
die are wire-bonded onto target pads on the flex PCB. These target
pads are located beside the die. The wire-bonds are then
encapsulated to prevent corrosion. Two non-plated holes 626 in the
flex PCB next to the die 628 are used to align the PCB to the
optical barrel 492. The optical barrel is then glued in place to
provide a seal around the image sensor 470. The horizontal
positional tolerance between the centre of the optical path and the
centre of the imaging area on the Jupiter die 628 is +/-50 microns.
The vertical tolerance due to the thickness of the die, the
thickness of the glue layer and the alignment of the optical barrel
492 to the front of the flex PCB 496 is +/-5 microns. In order to
the confined space at the front of the pen, the Jupiter die 628 is
designed so that the pads required for connection in the Netpage
pen are placed down opposite sides of the die.
Pod and External Cables
[0500] There are three main functions that are required by the pod
and external cabling. They are: [0501] provide a charging voltage
so that the pen can recharge its battery, [0502] provide a relay
mechanism for transferring stored digital ink to the Netpage server
via its Bluetooth/USB adapter and [0503] provide a relay mechanism
for downloading new program code to the pen via its Bluetooth/USB
adapter. Pod
[0504] Again referring to FIGS. 31 and 32, when the pen 400 is
inserted into the pod 450, power is provided by way of two sprung
contacts 516 in the pod which connect to the two coaxial conductive
tubes 498 that hold the ink cartridge tube 536 in the pen. The
power for the pod 450 and the pen 400 charging is provided by USB
bus power.
[0505] The pod has a tethered cable 572 which ends in two
connectors. One is a USB "A" plug. The other is a 4-way jack
socket. This 4-way jack socket is the same one present at the top
of the pen (see socket 458 in FIG. 15). When the 4-way jack is
inserted into the pod's cable, it provides power for the pod and to
the pen for charging. Otherwise, the power for the pod and the pen
charging is provided by the USB bus power.
[0506] Three indicator LEDs 452 are present in the pod. They
indicate the status of pen charging and communications.
Pod PCB
[0507] The pod PCB 560 contains a CSR BlueCore4-External device.
This is the same type of Bluetooth device as used in the pen 400.
The BlueCore4 device functions as a USB to Bluetooth bridge.
Cabling
[0508] Three cables are provided with the pen. The first cable 572
is tethered to the pod. At the other end of the cable is a USB A
connector and a 4-way jack socket. There are six wires going into
the pod, the four USB wires and two from the 4-way jack socket.
[0509] The second cable is a USB cable 462 (FIG. 15) with a USB A
connector on one end and a 4-way jack on the other end. The 4-way
jack can be connected to either the pod or the top of the pen.
[0510] The third cable is a plug pack power cable (not shown) which
plugs into a power outlet at one end and has a 4-way jack on the
other end. This 4-way jack can be connected to either the pod 450
or the top of the pen 456.
Connection Options
[0511] FIG. 61 shows the main charging and connection options for
the pen and pod: [0512] Option 1 shows a USB connection from a host
630 to the pod 450. The pen 400 is in the pod 450. The pod 450 and
the pen 400 communicate via Bluetooth. The pod is powered by the
USB bus power. The pen is charged from the USB bus power. As a
result the maximum USB power of 500 mA must be available in order
to charge the pen. [0513] Option 2 shows a USB connection from the
host 630 to the pod 450 and a plug pack 632 attached to the pod
cable 572. The pen 400 is in the pod 450. The pod and the pen
communicate via Bluetooth. The pod is powered by the plug pack. The
pen is charged from the plug pack power. [0514] Option 3 shows a
USB connection from the host 630 to the pod 450 and a plug pack 632
attached to the pen 400. The pen 400 is in the pod 450. The pod and
the pen communicate via Bluetooth. The pod is powered by the USB
bus power. The pen is charged from the plug pack power. [0515]
Option 4 shows a plug pack 632 attached to the pod cable 572. The
pen 400 is in the pod 450. There is no communication possible
between the pod and the pen. The pod is powered by the plug pack.
The pen is charged from the plug pack power. [0516] Option 5 shows
a USB connection from the host 630 to the pen 400. The pen 400 is
not in the pod 450. The host 630 and the pen 400 communicate via
USB, allowing a wired, non-RF communication link. The pen is
charged from the USB bus power. As a result the maximum USB power
of 500 mA must be available in order to charge the pen. [0517]
Option 6 shows the plug pack 632 attached to the pen 400. The pen
400 is not in the pod 450. The pen is charged from the plug pack
power. [0518] Other connection options are not shown. However, it
should be kept in mind that the pod is powered via its 4-way jack
connector (and not from the USB bus power) if there is a connector
in this jack. Also, the pen is powered from its 4-way jack (and not
from its pod connection) when there is a connector in this jack.
Battery and Power Consumption Referring to FIG. 68, the pen 400
contains a Lithium polymer battery 424 with a nominal capacity of
340 mAh. It's dimensions are 90.5 mm long.times.12 mm
wide.times.4.5 mm thick.
[0519] Based on the pen design, Table 4 shows the current
requirements for various pen and Bluetooth states. TABLE-US-00008
TABLE 4 Battery drain currents for all Pen states. Total mA @ State
Notes VBatt.sup.1 Pen Capped Pen is off 0.110 Pen Active Pen Down
92.7 Pen Hover-1 Pen up, trying to decoded tags 31.7 Pen Hover-2
Pen up, decoding tags 62.9 Pen Idle Pen up, not trying to decode
tags 28.8 Bluetooth Not Connected Bluetooth IC off 0.0 Bluetooth
Connection Bluetooth connected in low power, no digital ink 0.6
Timeout to download Bluetooth Connected Bluetooth connected in low
power Sniff state 4.1 (Sniff) Bluetooth Connected Bluetooth
connected in high power Active state 50.1 (Active) Bluetooth
Connecting Bluetooth trying to connect Network Access 15.1 Point
.sup.1Sum of all current drains at battery. The Bluetooth currents
can be concurrent with and additive to the Pen-state currents.
Pen Usage Scenarios
[0520] Some general usage scenarios are summarised here, showing
the energy requirements needed to fulfil these scenarios.
Worst Case Scenario
[0521] Summary: The pen is used intensively for 4 hours (cursive
writing) and will sit capped for one month (31 days), trying to
offload stored digital ink.
[0522] The energy requirement for this scenario is 968 mAh. The
nominal 340 mAh hour battery would achieve 35% of energy
requirement for this scenario.
Single Working Week Case Scenario
[0523] Summary: The pen is used for cursive writing for a total of
one hour a day for five days and is capped for the remaining time.
Total time for scenario is seven days.
[0524] The energy requirement for this scenario is 456 mAh. The
nominal 340 mAh hour battery would achieve 75% of energy
requirement for this scenario.
Single Working Week Not Capped During Working Hours Case
Scenario
[0525] Summary: The pen is used for cursive writing for a total of
one hour a day for five days and is capped for the remaining time.
Total time for scenario is seven days.
[0526] The energy requirement for this scenario is 1561 mAh. The
nominal 340 mAh hour battery would achieve 22% of energy
requirement for this scenario.
Software Design
Netpage Pen Software Overview
[0527] The Netpage pen software comprises that software running on
microprocessors in the Netpage pen 400 and Netpage pod 450.
[0528] The pen contains a number of microprocessors, as detailed in
the Electronics Design section described above. The Netpage pen
software includes software running on the Atmel ARM7 CPU 574
(hereafter CPU), the Force Sensor microprocessor 582, and also
software running in the VM on the CSR BlueCore Bluetooth module 578
(hereafter pen BlueCore). Each of these processors has an
associated flash memory which stores the processor specific
software, together with settings and other persistent data. The pen
BlueCore 578 also runs firmware supplied by the module
manufacturer, and this firmware is not considered a part of the
Netpage pen software.
[0529] The pod 450 contains a CSR BlueCore Bluetooth module
(hereafter pod BlueCore). The Netpage pen software also includes
software running in the VM on the pod BlueCore.
[0530] As the Netpage pen 400 traverses a Netpage tagged surface
548, a stream of correlated position and force samples are produced
(see Netpage Overview above). This stream is referred to as DInk.
Note that DInk may include samples with zero force (so called
"Hover DInk") produced when the Netpage pen is in proximity to, but
not marking, a Netpage tagged surface.
[0531] The CPU component of the Netpage pen software is responsible
for DInk capture, tag image processing and decoding (in conjunction
with the Jupiter image sensor 576), storage and offload management,
host communications, user feedback and software upgrade. It
includes an operating system (RTOS) and relevant hardware drivers.
In addition, it provides a manufacturing and maintenance mode for
calibration, configuration or detailed (non-field) fault diagnosis.
The Force Sensor microprocessor 582 component of the Netpage pen
software is responsible for filtering and preparing force samples
for the main CPU. The pen BlueCore VM software is responsible for
bridging the CPU UART 588 interface to USB when the pen is
operating in tethered mode. The pen BlueCore VM software is not
used when the pen is operating in Bluetooth mode.
[0532] The pod BlueCore VM software is responsible for sensing when
the pod 450 is charging a pen 400, controlling the pod LEDs 452
appropriately, and communicating with the host PC via USB.
[0533] A more detailed description of the software modules is set
out below.
[0534] The Netpage pen software is field upgradable, with the
exception of the initial boot loader. The field upgradable portion
does include the software running on the Force Sensor
microprocessor 582. Software upgrades are delivered to the pen via
its normal communication mechanisms (Bluetooth or USB). After being
received and validated, a new software image will be installed on
the next shutdown/startup cycle when the pen contains no DInk
pending offload.
Netpage System Overview
[0535] The Netpage pen software is designed to operate in
conjunction with a larger software system, comprising Netpage
relays and Netpage servers. The following is a brief overview of
these systems in relation to the Netpage pen--a detailed discussion
of the software for these systems and the specification of its
interface to Netpage pen software is set out in the cross
referenced documents.
[0536] Netpage relays are responsible for receiving DInk from pens,
and transmitting that DInk to Netpage servers or local
applications. The relay is a trusted service running on a device
trusted by the pen (paired in Bluetooth terminology). The relay
provides wide area networking services, bridging the gap between
the pen and DInk consumers (such as Netpage servers or other
applications). The primary relay device will be a desktop/laptop
computer equipped with a Netpage pod. Bluetooth equipped mobile
phones and PDAs can also be used as relays. Relays provide the pen
with access to WAN services by bridging the Bluetooth connection to
GPRS, WiFi or traditional wired LANs.
[0537] Netpage servers persist DInk permanently, and provide both
application services for DInk based applications (such as
handwriting recognition and form completion), and database
functionality for persisted DInk (such as search, retrieval and
reprinting).
[0538] Local applications may receive the DInk stream from the
Netpage relay and use it for application specific purposes (such as
for pointer replacement in image creation/manipulation
applications).
Internal Design
[0539] The Netpage pen software is divided into a number of major
modules: [0540] Image Processing [0541] DInk storage and offload
management [0542] Host Communications [0543] User Feedback [0544]
Power Management [0545] Software Upgrade [0546] Real Time Operating
System [0547] Hardware Drivers [0548] Manufacturing and Maintenance
mode [0549] Force Sensor Microprocessor software [0550] Pen
BlueCore VM software [0551] Pod BlueCore VM software
[0552] The remainder of this section gives a brief overview of
these major software modules.
Image Processing
[0553] The position information in the DInk stream produced by
traversing a Netpage tagged surface is produced by performing an
analysis of tagged images captured by the Jupiter Image Sensor
576.
[0554] The Image Processing module is responsible for analysing
images captured by Jupiter, identifying and decoding tags,
estimating the pose of the pen, and combining this information to
obtain position samples.
DInk Storage and Offload Management
[0555] Any DInk which corresponds to physical marking of a Netpage
tagged surface (e.g. excluding Hover DInk) must be reliably and
transactionally recorded by the Netpage system to allow for
accurate reproduction of the Netpage tagged surface. Ensuring such
DInk is recorded is the responsibility of the DInk storage and
offload management software. It persists DInk in flash memory on
the Netpage pen, and arranges for offload of DInk to a Netpage
server via a Netpage relay. This offload process is
transactional--the pen software maintains its record of DInk until
it can guarantee that DInk has been received and persisted by a
Netpage server.
[0556] DInk may be streamed in real time to applications requiring
real time response to DInk (for example applications which use the
pen as a replacement for a mouse or table pointer, such as graphics
editing applications). This may be normal DInk or Hover DInk (for
applications supporting hover), and the ability of the Netpage pen
software to stream DInk to such applications is orthogonal to the
storage and offload requirements for persistent DInk.
Host Communications
[0557] The Netpage pen software communicates with the Netpage relay
either through wireless Bluetooth communication, or through a wired
USB connection. Bluetooth connectivity is provided by the pen
BlueCore. USB connectivity is provided by using the Bluetooth
module in "pass through" mode.
[0558] The Communications module of the software is responsible for
reliably transmitting DInk from the DInk storage and offload
management module to the relay. It also provides management
functionality such as maintaining a persistent list of known,
trusted relays, and allows pairing with devices according to user
specification. The communications module includes third party
software (namely the ABCSP stack, see CSR, ABCSP Overview, AN11)
provided by CSR for communication with the pen BlueCore. Bluetooth
communication is only performed with Bluetooth paired devices, and
uses the Bluetooth encryption facilities to secure these
communications.
User Feedback
[0559] The Netpage pen provides two LEDs (red and green) and a
vibration motor for user feedback. The user feedback software
module is responsible for converting signals from other software
modules into user feedback using the provided mechanisms.
Power Management
[0560] The Netpage pen has a limited power budget, and its design
allows for dynamic power saving in a number of ways. For example,
the CPU can disable peripherals when they are not in use to save
power, and the pen BlueCore can be placed into a deep sleep mode or
powered down when it is not required. The CPU itself can be powered
down when the pen is not performing higher functions. Indeed, the
only always-on components are the Force Sensor microprocessor 582
and Power Management Chip 580 which can power on the CPU in
response to external stimuli. The Power Management module 580 is
responsible for analysing the current pen state and optimizing the
power usage by switching off un-needed peripherals and other
components as required. That is, this module intelligently manages
the facilities offered by the Power Management module to provide
optimal power usage given the required pen functionality.
Software Upgrade
[0561] The Netpage pen software is field upgradable, obtaining new
software images via its Bluetooth or USB connections. The Software
Upgrade module is responsible for managing the download of complete
images via the Communications module, validating these images
against included checksums, and arranging for the pen to boot from
a revised image when it has been validated.
[0562] The Software Upgrade process happens largely concurrently
with normal pen behaviour. The download of new images can happen
concurrently with normal pen operation and DInk offload. However,
the actual switch to boot from a new software image is only
performed when no outstanding DInk remains to be offloaded. This
simplifies management of the internal DInk formats, allowing them
to be upgraded as necessary in new software loads. Existing pairing
arrangements with relays are expected to survive software upgrade,
although under some circumstances it may be necessary to repeat
pairing operations.
[0563] It should also be noted that small parts of the Netpage pen
software, such as basic boot logic, are not field upgradable. These
parts of the software are minimal and tightly controlled.
[0564] Note that the Software Upgrade module also manages software
images for the Force Sensor microprocessor. Images for the latter
form a part of the Netpage pen software load, and the Software
Upgrade module reprograms the Force Sensor microprocessor in the
field when a new image contains revisions to the Force Sensor
microprocessor software.
Real Time Operating System
[0565] The Netpage pen software includes a Real Time Operating
System (RTOS) for efficient management of CPU resources. This
allows optimal handling of concurrent DInk capture, persistence,
and offload despite the latencies involved in image capture, flash
manipulation, and communication resources.
[0566] The RTOS for the Netpage pen software is the uC/OS II RTOS
from Micrium Systems (see Labrosse, J. L., MicroC OS II: The Real
Time Kernel, 2nd Edition, CMP Books, ISBN 1578201039). This part of
the Netpage pen software is comprised largely of third party code
supplied by Micrium, tailored and customized for the needs of the
pen.
Hardware Drivers
[0567] The Netpage pen software includes hardware drivers for all
peripherals (both internal to the CPU and external to it) required
for operation of the Netpage pen 400. This includes USRT 586, UART
588 and LSS 590 drivers for external bus communication, as well as
higher level drivers for managing the Jupiter Image Sensor 576, the
pen BlueCore 578, the Force Sensor microprocessor 582, the Power
Management IC 580, and other internal systems.
Manufacturing and Maintenance Mode
[0568] The Netpage pen 400 may be put into a special manufacturing
and maintenance mode for factory calibration or detailed non-field
failure analysis. A deployed pen will never enter manufacturing and
maintenance mode. It is a configuration, diagnostic and
rectification mode that is only expected to be used by Silverbrook
engineers under controlled conditions. The mechanism for placing
the Netpage pen software into maintenance mode is not described
here.
Force Sensor Microprocessor Software
[0569] The Force Sensor microprocessor 582 is an independent CPU
tasked with filtering and resampling the force data obtained from
the Force Sensor 500 proper to produce a stream of force samples to
be included into the DInk stream as recorded by the pen. It is also
responsible for initiating a wakeup of the CPU 574 in response to a
pen down, uncap, or timer event, in the case that the CPU has been
switched off for power saving purposes.
Pen BlueCore VM Software
[0570] The pen BlueCore is capable of running a small amount of
software in a virtual machine (VM). Such VM software is highly
resource limited, but can access the Bluetooth functionality, the
I/O ports, and a small number of GPIO pins on the pen BlueCore. A
small part of the Netpage pen software will run on the pen BlueCore
in order to manage bridging the CPU UART to the USB connection
provided by the pen BlueCore.
Pod BlueCore VM Software
[0571] The Netpage pod 450 contains a CSR BlueCore Bluetooth
module, but no general purpose microprocessor. The pod BlueCore
runs Netpage pen software in its VM. This software is responsible
for sensing when the pod 450 is charging a pen 400, controlling the
pod LEDs 452 to indicate charging and communications status, and
managing the USB communication link between the pod BlueCore and
the host PC. Note that BlueCore provides a split stack model for
the Bluetooth network stack, and the majority of the Bluetooth
network stack will in fact be running on the host PC (where it has
considerably greater access to resources).
Pen Assembly Sequence
[0572] The various sub-assemblies and components are manually
inserted into the pen chassis molding 416 (see FIG. 65). There are
no special tools required to insert any of the assemblies as there
is extensive use of snap fits and bumps on moldings for location.
The only assembly tool needed is a cold staking procedure required
after a testing to seal the pen assembly.
[0573] The assembly sequence for the pen is as follows:
Pen Chassis Assembly
[0574] The elastomeric end cap 460 is fed through an aperture 634
at the end of the chassis molding 416 and a tab 636 pulled through
to secure it in place.
Optics Assembly
[0575] The optics assembly sequence is as follows: [0576] The lens
is offered up to the aperture stop in the barrel and adhered in
place. [0577] The infrared filter is pushed into place in the front
of the barrel molding. [0578] The flex with image sensor is offered
up to the top of the barrel molding and accurately located onto two
pins. [0579] Epoxy is applied around the base of the barrel molding
to bond the flex into place and seal the image sensor from light
and particulate contaminants. Optics Assembly Insertion
[0580] As shown in FIG. 66A, the optics assembly 470 with the
unfolded flex PCB 496 protruding is inserted into the chassis
moulding 416 and snapped into place. The IR LEDs 434 and 436 are
then manipulated into cradles 638 either side of the barrel
moulding 492 as shown in FIG. 66B.
Force Sensing Assembly Insertion
[0581] As shown in FIGS. 67A and 67B, the force sensing assembly
474 is fed through between the chassis moulding 416 and the optical
barrel moulding 492. The assembly 474 is pivoted down and the force
sensor is secured in the correct orientation into the chassis
moulding between ribs 640 and a support detail 642.
[0582] The vibration motor 446 with elastomeric boot 644 is
assembled into an aperture in the chassis 416. The boot 644 has
negative draft on the support detail 642, which secures the motor
446 into the chassis 416 and orients it correctly.
[0583] A light pipe moulding 448 is placed into the chassis
moulding 416 and is a force fit.
PCB and Batter Insertion
[0584] The end of the optics flex PCB 496 is offered into the flex
connector 614 on the main PCB 422 and secured.
[0585] The main PCB 422 and LiPo battery 424 are then connected
together as the socket is on the upper side of the PCB 422 and is
not accessible when the board is in the chassis moulding 416. The
battery 424 has foam pads to protect the components on the lower
side of the PCB and to inhibit movement of the battery when it is
fully assembled. Referring to FIG. 69, the main PCB 422 and battery
424 can now be swung into place in the chassis moulding 416, with
care being taken not to unduly stress the flex PCB 496.
[0586] FIGS. 70A and 70B shows a cold stake tool 646 sealing a cold
stake pin 648 to an aperture 650 the base moulding 528. The cold
stake 648 is used to help locate the PCB 422 into the chassis
moulding 416 and with gentle pressure the walls of the chassis 416
expand enough to allow snap fits to engage with the PCB and hold it
securely. The PCB can still be extracted by flexing the chassis
walls in the same manner if necessary. The battery can be tacked in
place with adhesive tape if required.
[0587] The base moulding 528 is hinged onto the chassis moulding
416 and is fully located when the cold stake 648 appears in the
aperture 650.
Testing and Staking
[0588] At this point the assembly is complete enough to perform an
optical and electronic diagnostic test. If any problems occur, the
assembly can easily be stripped down again.
[0589] Once approved, a cold stake tool 646 is applied to the pin
648 from the chassis molding 416 swaging it over to hold the base
molding 528 captive (FIG. 70B). This prevents any user access to
internal parts.
Product Label
[0590] FIG. 71 shows a product label 652 being applied to the base
molding 416, which covers the cold stake 648. This label carries
all necessary product information for this class of digital mobile
product. It is exposed when the customisable tube molding 466 (see
FIG. 73) is removed by the user.
Nib Molding Assembly
[0591] As shown in FIG. 72, the nib molding 428 is offered up to
the pen assembly and is permanently snapped into place against the
chassis 416 and the base moldings 528 to form a sealed pen
unit.
Tube Molding Assembly
[0592] As shown in FIG. 73, the tube molding 466 is slid over the
pen assembly. The tube 466 is a transparent molding drafted from
the centre to allow for thin walls. An aquagraphic print is applied
to the surface with a mask used to retain a window 412, which looks
through to the light pipe 448 in the pen during use. A location
detail 656 on the chassis molding 416 provides positive feedback
when the molding is pushed home. The user can remove the tube
molding by holding the nib end and pulling without gaining access
to the pen assembly.
Cap Insertion
[0593] The cap assembly is fitted onto the pen to complete the
product as shown in FIG. 74.
Netpage Pen Major Power States
[0594] FIG. 75 shows the various power states that the pen can
adopt, as well as the pen functions during those power states.
Capped
[0595] In the Capped state 656, the Pen does not perform any
capture cycles.
[0596] Corresponding Pen Bluetooth states are Connected,
Connecting, Connection Timeout or Not Connected.
Hover1
[0597] In the Hover1 state 658, the Pen is performing very low
frequency capture cycles (of the order of 1 capture cycle per
second). Each capture cycle is tested for a valid decode, which
indicates that the user is attempting to use the Pen in hover
mode.
[0598] Valid Pen Bluetooth states are Connected or Connecting.
Hover2
[0599] In the Hover2 state 660, the Pen is performing capture
cycles of a lower frequency than in the Active state 662 (of the
order 50 capture cycles per second). Each capture cycle is tested
for a valid decode, which indicates that the user is continuing to
use the Pen in hover mode. After a certain number of failed
decodes, the Pen is no longer considered to be in hover mode.
[0600] Valid Pen Bluetooth states are Connected or Connecting.
Idle
[0601] In the Idle state 664, the Pen is not performing any capture
cycles, however, the Pen is active in as much as it is able to
start the first of a number of capture cycles within 5 ms of a pen
down event.
[0602] Valid Pen Bluetooth states are Connected or Connecting.
Active
[0603] In the Active state 662, the Pen is performing capture
cycles at full rate (100 capture cycles per second).
[0604] Valid Pen Bluetooth states are Connected or Connecting.
Netpage Pen Bluetooth States
[0605] FIG. 76 shows Netpage Pen power states that are related to
the Bluetooth wireless communications subsystem in order to respond
to digital ink offload requirements. Additionally, the Pen can
accept connections from devices in order to establish a Bluetooth
Pairing.
[0606] Each of the possible Pen Bluetooth related states are
described in the following sections.
Connected
[0607] In the Connected state 666 the primary task for the Pen is
to offload any digital ink that may be present within Pen storage,
or to stream digital ink as it is being captured. Whilst in the
Connected state it should also be possible for other devices to
discover and connect to the pen for the purposes of Bluetooth
Pairing.
[0608] In order to reduce power consumption whilst connected, it is
desirable to take advantage of the relatively low bandwidth
requirements of digital ink transmission and periodically enter a
Bluetooth low power mode. A useful low power mode will typically be
Sniff mode, wherein the periodic Bluetooth activity required of the
Pen is reduced based on the Sniff interval, with the Sniff interval
being determined by the current bandwidth requirements of digital
ink transmission.
Connecting
[0609] Whilst in the Connecting state 668, the Pen attempts to
establish a connection to one of a number of known NAPs (Network
Access Points) either to offload digital ink stored within Pen
memory, or in anticipation of a sequence of capture cycles.
[0610] Upon entry into the Connecting state 668, the Pen attempts
an Inquiry/Page of each device in round-robin fashion with a
relatively high frequency. If the connection is unsuccessful, the
frequency of Inquiry/Page is reduced successively in a number of
steps in order to reduce overall power consumption.
[0611] An Inquiry can last for 10.24 s and is repeated at a random
interval. Initially the Inquiry may be repeated on average at 5 s
intervals for the first 3 attempts, followed by 30 s for the next 5
attempts and then 5 minute intervals for the next 10 attempts and
10 minute intervals for subsequent attempts.
Connection Timeout
[0612] In the Connection Timeout state 670, the Pen maintains the
current Bluetooth connection by entering a Bluetooth low power
Sniff state with relatively long sniff interval (e.g. 2.56 seconds)
for a period of at least 2 minutes before disconnecting.
Re-establishment of the connection is not attempted, should the
connection be dropped before 2 minutes have elapsed.
Not Connected
[0613] In the Not Connected state 672, the Pen does not hold any
digital ink in its internal memory, and is capped. There is no
Bluetooth activity, and no Bluetooth connection exists.
Discoverable and Not Discoverable
[0614] The Pen is only discoverable 674 during the major states of
Hover1 658 and Idle 664. The Pen periodically enters the inquiry
scan and page scan states whilst in Hover1 658 or Idle 664, in
order to respond to connection requests from other devices.
Cap Detection Circuit
[0615] Referring once again to FIG. 26, a cap detection circuit
diagram is shown. As discussed above, the presence or absence of
the cap assembly 472 on the nib molding 428 can directly determine
the Pen power state and the Bluetooth state. The cap assembly 472
serves the dual purposes of protecting the nib 418 and the imaging
optics 426 when the pen 400 is not in use, and signalling, via its
removal or replacement, the pen to leave or enter a
power-preserving state.
[0616] As described in the `Pod Assembly` section above, the pen
400 has coaxial conductive tubes 498 that provide a set of external
contacts--power contacts 678 and data contacts 680. These mate with
contacts 516 in the pod 450 to provide the pen with charging power
and a USB connection. When placed over the nib molding 428, the
conductive elastomeric molding 522 short-circuits the pen's power
contacts 678 to signal the presence of the cap.
[0617] The pen has three capping states: [0618] cap on [0619] cap
off, not in pod [0620] cap off, in pod
[0621] In the cap on state, the CAP_ON signal 682 is high. The pen
will be powered off, subject to other pending activities such as
digital ink offload, as described above in the NetPage Pen
Bluetooth States section.
[0622] In the cap off, not in pod state, the CAP_ON signal 682 is
low. The pen will be powered on. In the cap off, in pod state, the
CAP_ON signal 682 is low. The pen will be powered on. The CAP_ON
signal 682 triggers transitions to and from the Capped state 656,
as described in the NetPage Pen Power States section above, via the
power management unit 580 and the Amtel ARM7 microprocessor 574
(see Pen Design section above).
[0623] The battery charger can use the VCHG signal 684 to charge
the battery. The VCHG signal 684 can be connected to the USB VBUS
voltage (nominally 5V) to allow the battery to be charged at up to
500 mA (based on the USB specification). The VCHG signal can also
be connected to a higher voltage generated by boosting the USB VBUS
voltage (maximum charging current would be lower than 500 mA).
Alternatively, the VCHG signal can be connected to a different
voltage, e.g. from a DC plug pack 632 (see Connection Options
section) connected to the pod 450. In this case, the pen is a
self-powered USB device from the point of view of the USB host
630.
[0624] When the cap assembly 472 is removed, the CAP_ON signal 682
is pulled low via transistor Q1 686. The switching time of Q1, and
hence the latency of cap removal detection, is a function of the
stray capacitance of Q1 and the value of resistor R1 688. A value
of 1 Mohm results in a latency of about 0.5 ms. The cap removal
detection latency must be balanced against the discharge rate of
the battery in the capped state. A value of 1 Mohm yields a trivial
discharge rate of 3 .mu.A. Diode D1 690 stops the battery being
charged from the VCHG voltage 684 through R1 688. The external USB
host 630 (see FIG. 61) is connected to the USB device 692 in the
pen 400 via the USB+ 694 and USB- 696 signals. Although the circuit
in FIG. 26 is shown with reference to a four-wire USB interface,
the cap detection function of the circuit only relates to the
two-wire power interface, and the pen can have a two-pin external
power interface rather than a four-pin external USB interface
depending on product configuration. The above description is purely
illustrative and the skilled worker in this field will readily
recognize many variations and modifications that do not depart from
the spirit and scope of the broad inventive concept.
* * * * *
References